diff --git a/apps/apps_container.cpp b/apps/apps_container.cpp
index 510cab5e7..255c90133 100644
--- a/apps/apps_container.cpp
+++ b/apps/apps_container.cpp
@@ -20,29 +20,23 @@ AppsContainer::AppsContainer() :
   m_batteryTimer(BatteryTimer(this)),
   m_USBTimer(USBTimer(this)),
   m_suspendTimer(SuspendTimer(this)),
-  m_backlightDimmingTimer(BacklightDimmingTimer())
+  m_backlightDimmingTimer(BacklightDimmingTimer()),
+  m_hardwareTestSnapshot(),
+  m_onBoardingSnapshot(),
+  m_homeSnapshot(),
+  m_calculationSnapshot(),
+  m_graphSnapshot(),
+  m_sequenceSnapshot(),
+  m_settingsSnapshot(),
+  m_statisticsSnapshot(),
+  m_probabilitySnapshot(),
+  m_regressionSnapshot()
 {
-  m_descriptors[0] = Home::App::buildDescriptor();
-  m_descriptors[1] = Calculation::App::buildDescriptor();
-  m_descriptors[2] = Graph::App::buildDescriptor();
-  m_descriptors[3] = Sequence::App::buildDescriptor();
-  m_descriptors[4] = Settings::App::buildDescriptor();
-  m_descriptors[5] = Statistics::App::buildDescriptor();
-  m_descriptors[6] = Probability::App::buildDescriptor();
-  m_descriptors[7] = Regression::App::buildDescriptor();
-  m_descriptors[8] = OnBoarding::App::buildDescriptor();
-  m_descriptors[9] = HardwareTest::App::buildDescriptor();
   refreshPreferences();
   m_emptyBatteryWindow.setFrame(KDRect(0, 0, Ion::Display::Width, Ion::Display::Height));
   Poincare::Expression::setCircuitBreaker(AppsContainer::poincareCircuitBreaker);
 }
 
-AppsContainer::~AppsContainer() {
-  for (int i = 0; i < k_totalNumberOfApps; i++) {
-    delete m_descriptors[i];
-  }
-}
-
 bool AppsContainer::poincareCircuitBreaker(const Poincare::Expression * e) {
   Ion::Keyboard::State state = Ion::Keyboard::scan();
   return Ion::Keyboard::keyDown(Ion::Keyboard::Key::A6, state);
@@ -52,22 +46,38 @@ int AppsContainer::numberOfApps() {
   return k_numberOfCommonApps;
 }
 
-App::Descriptor * AppsContainer::appDescriptorAtIndex(int index) {
+App::Snapshot * AppsContainer::appSnapshotAtIndex(int index) {
+  if (index < 0) {
+    return nullptr;
+  }
+  App::Snapshot * snapshots[] = {
+    &m_homeSnapshot,
+    &m_calculationSnapshot,
+    &m_graphSnapshot,
+    &m_sequenceSnapshot,
+    &m_settingsSnapshot,
+    &m_statisticsSnapshot,
+    &m_probabilitySnapshot,
+    &m_regressionSnapshot,
+  };
+  assert(sizeof(snapshots)/sizeof(snapshots[0]) == k_numberOfCommonApps);
   assert(index >= 0 && index < k_numberOfCommonApps);
-  return m_descriptors[index];
+  return snapshots[index];
 }
 
-App::Descriptor * AppsContainer::hardwareTestAppDescriptor() {
-  return m_descriptors[k_totalNumberOfApps-1];
+App::Snapshot * AppsContainer::hardwareTestAppSnapshot() {
+  return &m_hardwareTestSnapshot;
 }
 
-App::Descriptor * AppsContainer::onBoardingAppDescriptor() {
-  return m_descriptors[k_totalNumberOfApps - 2];
+App::Snapshot * AppsContainer::onBoardingAppSnapshot() {
+  return &m_onBoardingSnapshot;
 }
 
 void AppsContainer::reset() {
   Clipboard::sharedClipboard()->reset();
-  //TODO: persitence->reset()
+  for (int i = 0; i < k_numberOfCommonApps; i++) {
+    appSnapshotAtIndex(i)->reset();
+  }
 }
 
 Poincare::Context * AppsContainer::globalContext() {
@@ -83,7 +93,7 @@ VariableBoxController * AppsContainer::variableBoxController() {
 }
 
 void AppsContainer::suspend(bool checkIfPowerKeyReleased) {
-  if (activeApp()->descriptor() != onBoardingAppDescriptor() && GlobalPreferences::sharedGlobalPreferences()->showUpdatePopUp()) {
+  if (activeApp()->snapshot()!= onBoardingAppSnapshot() && GlobalPreferences::sharedGlobalPreferences()->showUpdatePopUp()) {
     activeApp()->displayModalViewController(&m_updateController, 0.f, 0.f);
   }
   Ion::Power::suspend(checkIfPowerKeyReleased);
@@ -103,12 +113,12 @@ bool AppsContainer::dispatchEvent(Ion::Events::Event event) {
   bool alphaLockWantsRedraw = m_window.updateAlphaLock();
 
   // Home and Power buttons are not sent to apps. We handle them straight away.
-  if (event == Ion::Events::Home && activeApp()->descriptor() != onBoardingAppDescriptor() && activeApp()->descriptor() != hardwareTestAppDescriptor() && activeApp()->descriptor() != appDescriptorAtIndex(0)) {
-    switchTo(appDescriptorAtIndex(0));
+  if (event == Ion::Events::Home && activeApp()->snapshot() != onBoardingAppSnapshot() && activeApp()->snapshot() != hardwareTestAppSnapshot()) {
+    switchTo(appSnapshotAtIndex(0));
     return true;
   }
-  if (event == Ion::Events::OnOff && activeApp()->descriptor() != hardwareTestAppDescriptor()) {
-    if (activeApp()->descriptor() == onBoardingAppDescriptor()) {
+  if (event == Ion::Events::OnOff && activeApp()->snapshot() != hardwareTestAppSnapshot()) {
+    if (activeApp()->snapshot() == onBoardingAppSnapshot()) {
       ((OnBoarding::App *)activeApp())->reinitOnBoarding();
     }
     suspend(true);
@@ -116,7 +126,7 @@ bool AppsContainer::dispatchEvent(Ion::Events::Event event) {
   }
   bool didProcessEvent = Container::dispatchEvent(event);
   if (!didProcessEvent && event == Ion::Events::Back) {
-    switchTo(appDescriptorAtIndex(0));
+    switchTo(appSnapshotAtIndex(0));
     return true;
   }
   if (!didProcessEvent && alphaLockWantsRedraw) {
@@ -126,17 +136,17 @@ bool AppsContainer::dispatchEvent(Ion::Events::Event event) {
   return didProcessEvent;
 }
 
-void AppsContainer::switchTo(App::Descriptor * descriptor) {
-  if (descriptor == hardwareTestAppDescriptor() || descriptor == onBoardingAppDescriptor()) {
+void AppsContainer::switchTo(App::Snapshot * snapshot) {
+  if (snapshot == hardwareTestAppSnapshot() || snapshot == onBoardingAppSnapshot()) {
     m_window.hideTitleBarView(true);
   } else {
     m_window.hideTitleBarView(false);
   }
-  if (descriptor) {
-    m_window.setTitle(descriptor->upperName());
+  if (snapshot) {
+    m_window.setTitle(snapshot->descriptor()->upperName());
   }
-  Container::switchTo(descriptor);
-  if (activeApp()->descriptor() == onBoardingAppDescriptor()) {
+  Container::switchTo(snapshot);
+  if (activeApp() != nullptr && activeApp()->snapshot() == onBoardingAppSnapshot()) {
     ((OnBoarding::App *)activeApp())->reinitOnBoarding();
   }
 }
@@ -178,12 +188,12 @@ Window * AppsContainer::window() {
 }
 
 int AppsContainer::numberOfTimers() {
-  bool onBoardingTimer = activeApp()->descriptor() == onBoardingAppDescriptor() && ((OnBoarding::App *)activeApp())->hasTimer();
+  bool onBoardingTimer = activeApp()->snapshot() == onBoardingAppSnapshot() && ((OnBoarding::App *)activeApp())->hasTimer();
   return 4+(GlobalPreferences::sharedGlobalPreferences()->examMode() == GlobalPreferences::ExamMode::Activate) + onBoardingTimer;
 }
 
 Timer * AppsContainer::timerAtIndex(int i) {
-  bool onBoardingTimer = activeApp()->descriptor() == onBoardingAppDescriptor() && ((OnBoarding::App *)activeApp())->hasTimer();
+  bool onBoardingTimer = activeApp()->snapshot() == onBoardingAppSnapshot() && ((OnBoarding::App *)activeApp())->hasTimer();
   if (onBoardingTimer && i == 4) {
     return ((OnBoarding::App *)activeApp())->timer();
   }
diff --git a/apps/apps_container.h b/apps/apps_container.h
index 7dd01c73e..6ea3d70b5 100644
--- a/apps/apps_container.h
+++ b/apps/apps_container.h
@@ -5,13 +5,13 @@
 #include "graph/app.h"
 #include "probability/app.h"
 #include "calculation/app.h"
-#include "hardware_test/app.h"
-#include "on_boarding/app.h"
-#include "on_boarding/update_controller.h"
 #include "regression/app.h"
 #include "sequence/app.h"
 #include "settings/app.h"
 #include "statistics/app.h"
+#include "on_boarding/app.h"
+#include "hardware_test/app.h"
+#include "on_boarding/update_controller.h"
 #include "apps_window.h"
 #include "empty_battery_window.h"
 #include "math_toolbox.h"
@@ -31,29 +31,18 @@
 class AppsContainer : public Container {
 public:
   AppsContainer();
-  ~AppsContainer();
-  /* Rule of 5: the copy constructor, move constructor, copy assignment
-   * operator and move assignment operator are deleted as their default
-   * implementation does not create new apps. The new object thus become
-   * obsolete as soon as the copy is deleted (because of our
-   * implementation of deletion). To avoid any use of obsolete object,
-   * we prevent to copy and assign. */
-  AppsContainer(const AppsContainer& other) = delete;
-  AppsContainer(AppsContainer&& other) = delete;
-  AppsContainer& operator=(const AppsContainer& other) = delete;
-  AppsContainer& operator=(AppsContainer&& other) = delete;
   static bool poincareCircuitBreaker(const Poincare::Expression * e);
   int numberOfApps();
-  App::Descriptor * appDescriptorAtIndex(int index);
-  App::Descriptor * hardwareTestAppDescriptor();
-  App::Descriptor * onBoardingAppDescriptor();
+  App::Snapshot * appSnapshotAtIndex(int index);
+  App::Snapshot * hardwareTestAppSnapshot();
+  App::Snapshot * onBoardingAppSnapshot();
   void reset();
   Poincare::Context * globalContext();
   MathToolbox * mathToolbox();
   VariableBoxController * variableBoxController();
   void suspend(bool checkIfPowerKeyReleased = false);
   virtual bool dispatchEvent(Ion::Events::Event event) override;
-  void switchTo(App::Descriptor * descriptor) override;
+  void switchTo(App::Snapshot * snapshot) override;
   void updateBatteryState();
   void refreshPreferences();
   void displayExamModePopUp(bool activate);
@@ -81,7 +70,16 @@ private:
   USBTimer m_USBTimer;
   SuspendTimer m_suspendTimer;
   BacklightDimmingTimer m_backlightDimmingTimer;
-  App::Descriptor * m_descriptors[k_totalNumberOfApps];
+  HardwareTest::App::Snapshot m_hardwareTestSnapshot;
+  OnBoarding::App::Snapshot m_onBoardingSnapshot;
+  Home::App::Snapshot m_homeSnapshot;
+  Calculation::App::Snapshot m_calculationSnapshot;
+  Graph::App::Snapshot m_graphSnapshot;
+  Sequence::App::Snapshot m_sequenceSnapshot;
+  Settings::App::Snapshot m_settingsSnapshot;
+  Statistics::App::Snapshot m_statisticsSnapshot;
+  Probability::App::Snapshot m_probabilitySnapshot;
+  Regression::App::Snapshot m_regressionSnapshot;
 };
 
 #endif
diff --git a/apps/calculation/app.cpp b/apps/calculation/app.cpp
index 2d3bd0b36..1ad45263a 100644
--- a/apps/calculation/app.cpp
+++ b/apps/calculation/app.cpp
@@ -2,16 +2,13 @@
 #include "../apps_container.h"
 #include "calculation_icon.h"
 #include "../i18n.h"
+
 using namespace Poincare;
 
 using namespace Shared;
 
 namespace Calculation {
 
-App * App::Descriptor::build(Container * container) {
-  return new App(container, this);
-}
-
 I18n::Message App::Descriptor::name() {
   return I18n::Message::CalculApp;
 }
@@ -24,17 +21,33 @@ const Image * App::Descriptor::icon() {
   return ImageStore::CalculationIcon;
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  TextFieldDelegateApp(container, &m_editExpressionController, descriptor),
-  m_localContext((GlobalContext *)((AppsContainer *)container)->globalContext(), &m_calculationStore),
-  m_calculationStore(),
-  m_historyController(&m_editExpressionController, &m_calculationStore),
-  m_editExpressionController(&m_modalViewController, &m_historyController, &m_calculationStore)
-{
+App * App::Snapshot::unpack(Container * container) {
+  return new App(container, this);
 }
 
-App::App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
+void App::Snapshot::reset() {
+  m_calculationStore.deleteAll();
+}
+
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+CalculationStore * App::Snapshot::calculationStore() {
+  return &m_calculationStore;
+}
+
+void App::Snapshot::tidy() {
+  m_calculationStore.tidy();
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  TextFieldDelegateApp(container, snapshot, &m_editExpressionController),
+  m_localContext((GlobalContext *)((AppsContainer *)container)->globalContext(), snapshot->calculationStore()),
+  m_historyController(&m_editExpressionController, snapshot->calculationStore()),
+  m_editExpressionController(&m_modalViewController, &m_historyController, snapshot->calculationStore())
+{
 }
 
 Context * App::localContext() {
diff --git a/apps/calculation/app.h b/apps/calculation/app.h
index c5dc6faf5..067c96c68 100644
--- a/apps/calculation/app.h
+++ b/apps/calculation/app.h
@@ -5,6 +5,7 @@
 #include "local_context.h"
 #include "history_controller.h"
 #include "../shared/text_field_delegate_app.h"
+#include "calculation_store.h"
 #include <escher.h>
 
 namespace Calculation {
@@ -13,17 +14,24 @@ class App : public Shared::TextFieldDelegateApp {
 public:
   class Descriptor : public ::App::Descriptor {
   public:
-    App * build(Container * container) override;
     I18n::Message name() override;
     I18n::Message upperName() override;
     const Image * icon() override;
   };
-  static Descriptor * buildDescriptor();
+  class Snapshot : public ::App::Snapshot {
+  public:
+    App * unpack(Container * container) override;
+    void reset() override;
+    Descriptor * descriptor() override;
+    CalculationStore * calculationStore();
+  private:
+    void tidy() override;
+    CalculationStore m_calculationStore;
+  };
   Poincare::Context * localContext() override;
 private:
-  App(Container * container, Descriptor * descriptor);
+  App(Container * container, Snapshot * snapshot);
   LocalContext m_localContext;
-  CalculationStore m_calculationStore;
   HistoryController m_historyController;
   EditExpressionController m_editExpressionController;
 };
diff --git a/apps/calculation/calculation.cpp b/apps/calculation/calculation.cpp
index ae3aea970..93eab7d9a 100644
--- a/apps/calculation/calculation.cpp
+++ b/apps/calculation/calculation.cpp
@@ -34,6 +34,59 @@ Calculation::~Calculation() {
 void Calculation::reset() {
   m_inputText[0] = 0;
   m_outputText[0] = 0;
+  tidy();
+}
+
+void Calculation::setContent(const char * c, Context * context) {
+  reset();
+  strlcpy(m_inputText, c, sizeof(m_inputText));
+  output(context)->writeTextInBuffer(m_outputText, sizeof(m_outputText));
+}
+
+const char * Calculation::inputText() {
+  return m_inputText;
+}
+
+const char * Calculation::outputText() {
+  return m_outputText;
+}
+
+Expression * Calculation::input() {
+  if (m_input == nullptr) {
+    m_input = Expression::parse(m_inputText);
+  }
+  return m_input;
+}
+
+ExpressionLayout * Calculation::inputLayout() {
+  if (m_inputLayout == nullptr && input() != nullptr) {
+    m_inputLayout = input()->createLayout(Expression::FloatDisplayMode::Decimal, Expression::ComplexFormat::Algebric);
+  }
+  return m_inputLayout;
+}
+
+Expression * Calculation::output(Context * context) {
+  if (m_output == nullptr && input() != nullptr) {
+    m_output = input()->evaluate(*context);
+  }
+  return m_output;
+}
+
+ExpressionLayout * Calculation::outputLayout(Context * context) {
+  if (m_outputLayout == nullptr && output(context) != nullptr) {
+    m_outputLayout = output(context)->createLayout();
+  }
+  return m_outputLayout;
+}
+
+bool Calculation::isEmpty() {
+  if (strlen(m_inputText) == 0) {
+    return true;
+  }
+  return false;
+}
+
+void Calculation::tidy() {
   if (m_input != nullptr) {
     delete m_input;
   }
@@ -52,45 +105,4 @@ void Calculation::reset() {
   m_outputLayout = nullptr;
 }
 
-void Calculation::setContent(const char * c, Context * context) {
-  reset();
-  strlcpy(m_inputText, c, sizeof(m_inputText));
-  m_input = Expression::parse(m_inputText);
-  m_inputLayout = m_input->createLayout(Expression::FloatDisplayMode::Decimal, Expression::ComplexFormat::Algebric);
-  m_output = m_input->evaluate(*context);
-  m_outputLayout = m_output->createLayout();
-  m_output->writeTextInBuffer(m_outputText, sizeof(m_outputText));
-}
-
-const char * Calculation::inputText() {
-  return m_inputText;
-}
-
-const char * Calculation::outputText() {
-  return m_outputText;
-}
-
-Expression * Calculation::input() {
-  return m_input;
-}
-
-ExpressionLayout * Calculation::inputLayout() {
-  return m_inputLayout;
-}
-
-Expression * Calculation::output() {
-  return m_output;
-}
-
-ExpressionLayout * Calculation::outputLayout() {
-  return m_outputLayout;
-}
-
-bool Calculation::isEmpty() {
-  if (m_output == nullptr) {
-    return true;
-  }
-  return false;
-}
-
 }
diff --git a/apps/calculation/calculation.h b/apps/calculation/calculation.h
index 8ee6c72e8..571e2300b 100644
--- a/apps/calculation/calculation.h
+++ b/apps/calculation/calculation.h
@@ -20,10 +20,11 @@ public:
   const char * outputText();
   Poincare::Expression * input();
   Poincare::ExpressionLayout * inputLayout();
-  Poincare::Expression * output();
-  Poincare::ExpressionLayout * outputLayout();
+  Poincare::Expression * output(Poincare::Context * context);
+  Poincare::ExpressionLayout * outputLayout(Poincare::Context * context);
   void setContent(const char * c, Poincare::Context * context);
   bool isEmpty();
+  void tidy();
 private:
   char m_inputText[::TextField::maxBufferSize()];
   char m_outputText[::TextField::maxBufferSize()];
diff --git a/apps/calculation/calculation_store.cpp b/apps/calculation/calculation_store.cpp
index cfe8b2aa1..34ab18c89 100644
--- a/apps/calculation/calculation_store.cpp
+++ b/apps/calculation/calculation_store.cpp
@@ -61,4 +61,10 @@ void CalculationStore::deleteAll() {
   }
 }
 
+void CalculationStore::tidy() {
+  for (int i = 0; i < k_maxNumberOfCalculations; i++) {
+    m_calculations[i].tidy();
+  }
+}
+
 }
diff --git a/apps/calculation/calculation_store.h b/apps/calculation/calculation_store.h
index d8f436fad..0348c1844 100644
--- a/apps/calculation/calculation_store.h
+++ b/apps/calculation/calculation_store.h
@@ -15,6 +15,7 @@ public:
   void deleteCalculationAtIndex(int i);
   void deleteAll();
   int numberOfCalculations();
+  void tidy();
 private:
   static constexpr int k_maxNumberOfCalculations = 10;
   Calculation * m_start;
diff --git a/apps/calculation/history_controller.cpp b/apps/calculation/history_controller.cpp
index 5c7f8eaf2..474bea9cd 100644
--- a/apps/calculation/history_controller.cpp
+++ b/apps/calculation/history_controller.cpp
@@ -108,7 +108,6 @@ void HistoryController::tableViewDidChangeSelection(SelectableTableView * t, int
   if (selectedCell == nullptr) {
     return;
   }
-  selectedCell->setParentResponder(t);
   if (selectedRow() < previousSelectedCellY) {
     selectedCell->setSelectedSubviewType(HistoryViewCell::SubviewType::Output);
   }
@@ -147,7 +146,8 @@ void HistoryController::willDisplayCellForIndex(HighlightCell * cell, int index)
 KDCoordinate HistoryController::rowHeight(int j) {
   Calculation * calculation = m_calculationStore->calculationAtIndex(j);
   KDCoordinate inputHeight = calculation->inputLayout()->size().height();
-  KDCoordinate outputHeight = calculation->outputLayout()->size().height();
+  App * calculationApp = (App *)app();
+  KDCoordinate outputHeight = calculation->outputLayout(calculationApp->localContext())->size().height();
   return inputHeight + outputHeight + 3*HistoryViewCell::k_digitVerticalMargin;
 }
 
@@ -181,10 +181,11 @@ CalculationSelectableTableView * HistoryController::selectableTableView() {
 }
 
 View * HistoryController::loadView() {
-  for (int i = 0; i < k_maxNumberOfDisplayedRows; i++) {
-    m_calculationHistory[i] = new HistoryViewCell();
+  CalculationSelectableTableView * tableView = new CalculationSelectableTableView(this, this, this);
+for (int i = 0; i < k_maxNumberOfDisplayedRows; i++) {
+    m_calculationHistory[i] = new HistoryViewCell(tableView);
   }
-  return new CalculationSelectableTableView(this, this, this);
+  return tableView;
 }
 
 void HistoryController::unloadView(View * view) {
diff --git a/apps/calculation/history_view_cell.cpp b/apps/calculation/history_view_cell.cpp
index c763165ea..671de7047 100644
--- a/apps/calculation/history_view_cell.cpp
+++ b/apps/calculation/history_view_cell.cpp
@@ -1,4 +1,5 @@
 #include "history_view_cell.h"
+#include "app.h"
 #include "../constant.h"
 #include "selectable_table_view.h"
 #include <assert.h>
@@ -6,8 +7,8 @@
 
 namespace Calculation {
 
-HistoryViewCell::HistoryViewCell() :
-  Responder(nullptr),
+HistoryViewCell::HistoryViewCell(Responder * parentResponder) :
+  Responder(parentResponder),
   m_inputView(this),
   m_outputView(this),
   m_selectedSubviewType(HistoryViewCell::SubviewType::Output)
@@ -48,7 +49,8 @@ void HistoryViewCell::layoutSubviews() {
 
 void HistoryViewCell::setCalculation(Calculation * calculation) {
   m_inputView.setExpression(calculation->inputLayout());
-  m_outputView.setExpression(calculation->outputLayout());
+  App * calculationApp = (App *)app();
+  m_outputView.setExpression(calculation->outputLayout(calculationApp->localContext()));
 }
 
 void HistoryViewCell::reloadCell() {
diff --git a/apps/calculation/history_view_cell.h b/apps/calculation/history_view_cell.h
index 046e38a2f..048613ec9 100644
--- a/apps/calculation/history_view_cell.h
+++ b/apps/calculation/history_view_cell.h
@@ -13,7 +13,7 @@ public:
     Input,
     Output
   };
-  HistoryViewCell();
+  HistoryViewCell(Responder * parentResponder);
   void reloadCell() override;
   KDColor backgroundColor() const override;
   void setCalculation(Calculation * calculation);
diff --git a/apps/calculation/local_context.cpp b/apps/calculation/local_context.cpp
index 1b4a363c7..f0352b2e3 100644
--- a/apps/calculation/local_context.cpp
+++ b/apps/calculation/local_context.cpp
@@ -15,7 +15,7 @@ Expression * LocalContext::ansValue() {
     return m_parentContext->defaultExpression();
   }
   Calculation * lastCalculation = m_calculationStore->calculationAtIndex(m_calculationStore->numberOfCalculations()-1);
-  return lastCalculation->output();
+  return lastCalculation->output(m_parentContext);
 }
 
 void LocalContext::setExpressionForSymbolName(Expression * expression, const Symbol * symbol) {
diff --git a/apps/graph/app.cpp b/apps/graph/app.cpp
index a65ad761d..7e3337edb 100644
--- a/apps/graph/app.cpp
+++ b/apps/graph/app.cpp
@@ -8,10 +8,6 @@ using namespace Shared;
 
 namespace Graph {
 
-App * App::Descriptor::build(Container * container) {
-  return new App(container, this);
-}
-
 I18n::Message App::Descriptor::name() {
   return I18n::Message::FunctionApp;
 }
@@ -24,19 +20,39 @@ const Image * App::Descriptor::icon() {
   return ImageStore::GraphIcon;
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  FunctionApp(container,  &m_inputViewController, descriptor),
-  m_functionStore(),
+App * App::Snapshot::unpack(Container * container) {
+  return new App(container, this);
+}
+
+void App::Snapshot::reset() {
+  m_functionStore.removeAll();
+}
+
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+CartesianFunctionStore * App::Snapshot::functionStore() {
+  return &m_functionStore;
+}
+
+void App::Snapshot::tidy() {
+  m_functionStore.tidy();
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  FunctionApp(container, snapshot, &m_inputViewController),
   m_xContext('x',((AppsContainer *)container)->globalContext()),
-  m_listController(&m_listFooter, &m_functionStore, &m_listHeader, &m_listFooter),
+  m_listController(&m_listFooter, snapshot->functionStore(), &m_listHeader, &m_listFooter),
   m_listFooter(&m_listHeader, &m_listController, &m_listController, ButtonRowController::Position::Bottom, ButtonRowController::Style::EmbossedGrey),
   m_listHeader(&m_listStackViewController, &m_listFooter, &m_listController),
   m_listStackViewController(&m_tabViewController, &m_listHeader),
-  m_graphController(&m_graphAlternateEmptyViewController, &m_functionStore, &m_graphHeader),
+  m_graphController(&m_graphAlternateEmptyViewController, snapshot->functionStore(), &m_graphHeader),
   m_graphAlternateEmptyViewController(&m_graphHeader, &m_graphController, &m_graphController),
   m_graphHeader(&m_graphStackViewController, &m_graphAlternateEmptyViewController, &m_graphController),
   m_graphStackViewController(&m_tabViewController, &m_graphHeader),
-  m_valuesController(&m_valuesAlternateEmptyViewController, &m_functionStore, &m_valuesHeader),
+  m_valuesController(&m_valuesAlternateEmptyViewController, snapshot->functionStore(), &m_valuesHeader),
   m_valuesAlternateEmptyViewController(&m_valuesHeader, &m_valuesController, &m_valuesController),
   m_valuesHeader(&m_valuesStackViewController, &m_valuesAlternateEmptyViewController, &m_valuesController),
   m_valuesStackViewController(&m_tabViewController, &m_valuesHeader),
@@ -45,10 +61,6 @@ App::App(Container * container, Descriptor * descriptor) :
 {
 }
 
-App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
-}
-
 InputViewController * App::inputViewController() {
   return &m_inputViewController;
 }
diff --git a/apps/graph/app.h b/apps/graph/app.h
index 58c8f4bc9..c3cd58129 100644
--- a/apps/graph/app.h
+++ b/apps/graph/app.h
@@ -15,12 +15,20 @@ class App : public Shared::FunctionApp {
 public:
   class Descriptor : public ::App::Descriptor {
   public:
-    App * build(Container * container) override;
     I18n::Message name() override;
     I18n::Message upperName() override;
     const Image * icon() override;
   };
-  static Descriptor * buildDescriptor();
+  class Snapshot : public ::App::Snapshot {
+  public:
+    App * unpack(Container * container) override;
+    void reset() override;
+    Descriptor * descriptor() override;
+    CartesianFunctionStore * functionStore();
+  private:
+    void tidy() override;
+    CartesianFunctionStore m_functionStore;
+  };
   InputViewController * inputViewController() override;
   /* This local context can parse x. However, it always stores NAN
    * as x value. When we need to evaluate expression with a specific x value, we
@@ -28,8 +36,7 @@ public:
    * weird x values after drawing curves or displaying the value table. */
   Poincare::Context * localContext() override;
 private:
-  App(Container * container, Descriptor * descriptor);
-  CartesianFunctionStore m_functionStore;
+  App(Container * container, Snapshot * snapshot);
   Poincare::VariableContext m_xContext;
   ListController m_listController;
   ButtonRowController m_listFooter;
diff --git a/apps/graph/graph/curve_parameter_controller.cpp b/apps/graph/graph/curve_parameter_controller.cpp
index b98686e85..dd10280fb 100644
--- a/apps/graph/graph/curve_parameter_controller.cpp
+++ b/apps/graph/graph/curve_parameter_controller.cpp
@@ -1,4 +1,5 @@
 #include "curve_parameter_controller.h"
+#include "../../i18n.h"
 #include <assert.h>
 
 using namespace Shared;
diff --git a/apps/hardware_test/app.cpp b/apps/hardware_test/app.cpp
index 6ce7b02d5..bb7c6fbb8 100644
--- a/apps/hardware_test/app.cpp
+++ b/apps/hardware_test/app.cpp
@@ -7,18 +7,19 @@ extern "C" {
 
 namespace HardwareTest {
 
-App * App::Descriptor::build(Container * container) {
+App * App::Snapshot::unpack(Container * container) {
   return new App(container, this);
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  ::App(container, &m_keyboardController, descriptor),
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  ::App(container, snapshot, &m_keyboardController),
   m_keyboardController(&m_modalViewController)
 {
 }
 
-App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
-}
-
 }
diff --git a/apps/hardware_test/app.h b/apps/hardware_test/app.h
index 2c67bd694..70f72ca80 100644
--- a/apps/hardware_test/app.h
+++ b/apps/hardware_test/app.h
@@ -10,13 +10,13 @@ namespace HardwareTest {
 
 class App : public ::App {
 public:
-  class Descriptor : public ::App::Descriptor {
+  class Snapshot : public ::App::Snapshot {
   public:
-    App * build(Container * container) override;
+    App * unpack(Container * container) override;
+    Descriptor * descriptor() override;
   };
-  static Descriptor * buildDescriptor();
 private:
-  App(Container * container, Descriptor * descriptor);
+  App(Container * container, Snapshot * snapshot);
   KeyboardController m_keyboardController;
 };
 
diff --git a/apps/hardware_test/color_controller.cpp b/apps/hardware_test/color_controller.cpp
index a7557ae93..c5c3d38d7 100644
--- a/apps/hardware_test/color_controller.cpp
+++ b/apps/hardware_test/color_controller.cpp
@@ -20,7 +20,7 @@ bool ColorController::handleEvent(Ion::Events::Event event) {
   m_view.setColors(nextColor(m_view.fillColor()), nextColor(m_view.outlineColor()));
   if (m_view.fillColor() == KDColorBlack) {
     AppsContainer * container = (AppsContainer *)app()->container();
-    container->switchTo(container->appDescriptorAtIndex(0));
+    container->switchTo(container->appSnapshotAtIndex(0));
   }
   return true;
 }
diff --git a/apps/home/app.cpp b/apps/home/app.cpp
index 3117414ff..57b90dc1c 100644
--- a/apps/home/app.cpp
+++ b/apps/home/app.cpp
@@ -1,6 +1,6 @@
 #include "app.h"
-#include "../apps_container.h"
 #include "../i18n.h"
+#include "../apps_container.h"
 
 extern "C" {
 #include <assert.h>
@@ -8,10 +8,6 @@ extern "C" {
 
 namespace Home {
 
-App * App::Descriptor::build(Container * container) {
-  return new App(container, this);
-}
-
 I18n::Message App::Descriptor::name() {
   return I18n::Message::Apps;
 }
@@ -20,14 +16,19 @@ I18n::Message App::Descriptor::upperName() {
   return I18n::Message::AppsCapital;
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  ::App(container, &m_controller, descriptor, I18n::Message::Warning),
+App * App::Snapshot::unpack(Container * container) {
+  return new App(container, this);
+}
+
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  ::App(container, snapshot, &m_controller, I18n::Message::Warning),
   m_controller(&m_modalViewController, (AppsContainer *)container)
 {
 }
 
-App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
-}
-
 }
diff --git a/apps/home/app.h b/apps/home/app.h
index 6af9f4d49..dee11daf7 100644
--- a/apps/home/app.h
+++ b/apps/home/app.h
@@ -12,13 +12,16 @@ class App : public ::App {
 public:
   class Descriptor : public ::App::Descriptor {
   public:
-    App * build(Container * container) override;
     I18n::Message name() override;
     I18n::Message upperName() override;
   };
-  static Descriptor * buildDescriptor();
+  class Snapshot : public ::App::Snapshot {
+  public:
+    App * unpack(Container * container) override;
+    Descriptor * descriptor() override;
+  };
 private:
-  App(Container * container, Descriptor * descriptor);
+  App(Container * container, Snapshot * snapshot);
   Controller m_controller;
 };
 
diff --git a/apps/home/controller.cpp b/apps/home/controller.cpp
index 139908950..bff5609d8 100644
--- a/apps/home/controller.cpp
+++ b/apps/home/controller.cpp
@@ -47,7 +47,7 @@ Controller::Controller(Responder * parentResponder, ::AppsContainer * container)
 
 bool Controller::handleEvent(Ion::Events::Event event) {
   if (event == Ion::Events::OK || event == Ion::Events::EXE) {
-    m_container->switchTo(m_container->appDescriptorAtIndex(selectedRow()*k_numberOfColumns+selectedColumn()+1));
+    m_container->switchTo(m_container->appSnapshotAtIndex(selectedRow()*k_numberOfColumns+selectedColumn()+1));
     return true;
   }
   return false;
@@ -101,7 +101,7 @@ void Controller::willDisplayCellAtLocation(HighlightCell * cell, int i, int j) {
     appCell->setVisible(false);
   } else {
     appCell->setVisible(true);
-    ::App::Descriptor * descriptor = m_container->appDescriptorAtIndex((j*k_numberOfColumns+i)+1);
+    ::App::Descriptor * descriptor = m_container->appSnapshotAtIndex((j*k_numberOfColumns+i)+1)->descriptor();
     appCell->setAppDescriptor(descriptor);
   }
 }
diff --git a/apps/main.cpp b/apps/main.cpp
index d32cff3b0..b1a64538d 100644
--- a/apps/main.cpp
+++ b/apps/main.cpp
@@ -3,7 +3,7 @@
 AppsContainer container;
 
 void ion_app() {
-  container.switchTo(container.onBoardingAppDescriptor());
+  container.switchTo(container.onBoardingAppSnapshot());
   container.run();
   container.switchTo(nullptr);
 }
diff --git a/apps/on_boarding/app.cpp b/apps/on_boarding/app.cpp
index d7b09f812..fd07c5b7a 100644
--- a/apps/on_boarding/app.cpp
+++ b/apps/on_boarding/app.cpp
@@ -3,21 +3,22 @@
 
 namespace OnBoarding {
 
-App * App::Descriptor::build(Container * container) {
+App * App::Snapshot::unpack(Container * container) {
   return new App(container, this);
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  ::App(container, &m_languageController, descriptor),
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  ::App(container, snapshot, &m_languageController),
   m_languageController(&m_modalViewController, &m_logoController, ((AppsContainer *)container)->updatePopUpController()),
   m_logoController()
 {
 }
 
-App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
-}
-
 void App::reinitOnBoarding() {
   m_languageController.reinitOnBoarding();
 }
diff --git a/apps/on_boarding/app.h b/apps/on_boarding/app.h
index 81f57ab64..108f64385 100644
--- a/apps/on_boarding/app.h
+++ b/apps/on_boarding/app.h
@@ -10,16 +10,16 @@ namespace OnBoarding {
 
 class App : public ::App {
 public:
-  class Descriptor : public ::App::Descriptor {
+  class Snapshot : public ::App::Snapshot {
   public:
-    App * build(Container * container) override;
+    App * unpack(Container * container) override;
+    Descriptor * descriptor() override;
   };
-  static Descriptor * buildDescriptor();
   void reinitOnBoarding();
   bool hasTimer();
   Timer * timer();
 private:
-  App(Container * container, Descriptor * descriptor);
+  App(Container * container, Snapshot * snapshot);
   LanguageController m_languageController;
   LogoController m_logoController;
 };
diff --git a/apps/on_boarding/update_controller.cpp b/apps/on_boarding/update_controller.cpp
index e37b53673..04ec7881c 100644
--- a/apps/on_boarding/update_controller.cpp
+++ b/apps/on_boarding/update_controller.cpp
@@ -16,8 +16,8 @@ bool UpdateController::handleEvent(Ion::Events::Event event) {
   if (event != Ion::Events::Back) {
     app()->dismissModalViewController();
     AppsContainer * appsContainer = (AppsContainer *)app()->container();
-    if (appsContainer->activeApp()->descriptor() == appsContainer->onBoardingAppDescriptor()) {
-      appsContainer->switchTo(appsContainer->appDescriptorAtIndex(0));
+    if (appsContainer->activeApp()->snapshot() == appsContainer->onBoardingAppSnapshot()) {
+      appsContainer->switchTo(appsContainer->appSnapshotAtIndex(0));
     }
     return true;
   }
diff --git a/apps/probability/app.cpp b/apps/probability/app.cpp
index 7af503ebf..8cb1dcc43 100644
--- a/apps/probability/app.cpp
+++ b/apps/probability/app.cpp
@@ -1,14 +1,11 @@
 #include "app.h"
+#include "../i18n.h"
 #include "probability_icon.h"
 
 using namespace Shared;
 
 namespace Probability {
 
-App * App::Descriptor::build(Container * container) {
-  return new App(container, this);
-}
-
 I18n::Message App::Descriptor::name() {
   return I18n::Message::ProbaApp;
 }
@@ -21,15 +18,20 @@ const Image * App::Descriptor::icon() {
   return ImageStore::ProbabilityIcon;
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  TextFieldDelegateApp(container, &m_stackViewController, descriptor),
+App * App::Snapshot::unpack(Container * container) {
+  return new App(container, this);
+}
+
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  TextFieldDelegateApp(container, snapshot, &m_stackViewController),
   m_lawController(nullptr),
   m_stackViewController(&m_modalViewController, &m_lawController)
 {
 }
 
-App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
-}
-
 }
diff --git a/apps/probability/app.h b/apps/probability/app.h
index f27bdcf7a..c0324f1c7 100644
--- a/apps/probability/app.h
+++ b/apps/probability/app.h
@@ -12,14 +12,17 @@ class App : public Shared::TextFieldDelegateApp {
 public:
   class Descriptor : public ::App::Descriptor {
   public:
-    App * build(Container * container) override;
     I18n::Message name() override;
     I18n::Message upperName() override;
     const Image * icon() override;
   };
-  static Descriptor * buildDescriptor();
+  class Snapshot : public ::App::Snapshot {
+  public:
+    App * unpack(Container * container) override;
+    Descriptor * descriptor() override;
+  };
 private:
-  App(Container * container, Descriptor * descriptor);
+  App(Container * container, Snapshot * snapshot);
   LawController m_lawController;
   StackViewController m_stackViewController;
 };
diff --git a/apps/probability/calculation_controller.cpp b/apps/probability/calculation_controller.cpp
index deffd982b..a3d4292c0 100644
--- a/apps/probability/calculation_controller.cpp
+++ b/apps/probability/calculation_controller.cpp
@@ -1,6 +1,7 @@
 #include "calculation_controller.h"
 #include "../constant.h"
 #include "../apps_container.h"
+#include "app.h"
 #include "calculation/left_integral_calculation.h"
 #include "calculation/right_integral_calculation.h"
 #include "calculation/finite_integral_calculation.h"
diff --git a/apps/regression/app.cpp b/apps/regression/app.cpp
index 5df331321..b656e60d5 100644
--- a/apps/regression/app.cpp
+++ b/apps/regression/app.cpp
@@ -6,10 +6,6 @@ using namespace Shared;
 
 namespace Regression {
 
-App * App::Descriptor::build(Container * container) {
-  return new App(container, this);
-}
-
 I18n::Message App::Descriptor::name() {
   return I18n::Message::RegressionApp;
 }
@@ -22,25 +18,38 @@ const Image * App::Descriptor::icon() {
   return ImageStore::RegressionIcon;
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  TextFieldDelegateApp(container, &m_tabViewController, descriptor),
-  m_store(),
-  m_calculationController(&m_calculationAlternateEmptyViewController, &m_calculationHeader, &m_store),
+App * App::Snapshot::unpack(Container * container) {
+  return new App(container, this);
+}
+
+void App::Snapshot::reset() {
+  m_store.deleteAllPairs();
+}
+
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+Store * App::Snapshot::store() {
+  return &m_store;
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  TextFieldDelegateApp(container, snapshot, &m_tabViewController),
+  m_calculationController(&m_calculationAlternateEmptyViewController, &m_calculationHeader, snapshot->store()),
   m_calculationAlternateEmptyViewController(&m_calculationHeader, &m_calculationController, &m_calculationController),
   m_calculationHeader(&m_tabViewController, &m_calculationAlternateEmptyViewController, &m_calculationController),
-  m_graphController(&m_graphAlternateEmptyViewController, &m_graphHeader, &m_store),
+  m_graphController(&m_graphAlternateEmptyViewController, &m_graphHeader, snapshot->store()),
   m_graphAlternateEmptyViewController(&m_graphHeader, &m_graphController, &m_graphController),
   m_graphHeader(&m_graphStackViewController, &m_graphAlternateEmptyViewController, &m_graphController),
   m_graphStackViewController(&m_tabViewController, &m_graphHeader),
-  m_storeController(&m_storeHeader, &m_store, &m_storeHeader),
+  m_storeController(&m_storeHeader, snapshot->store(), &m_storeHeader),
   m_storeHeader(&m_storeStackViewController, &m_storeController, &m_storeController),
   m_storeStackViewController(&m_tabViewController, &m_storeHeader),
   m_tabViewController(&m_modalViewController, &m_storeStackViewController, &m_graphStackViewController, &m_calculationHeader)
 {
 }
 
-App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
-}
 
 }
diff --git a/apps/regression/app.h b/apps/regression/app.h
index 0a16cf9dc..611658dac 100644
--- a/apps/regression/app.h
+++ b/apps/regression/app.h
@@ -14,15 +14,21 @@ class App : public Shared::TextFieldDelegateApp {
 public:
   class Descriptor : public ::App::Descriptor {
   public:
-    App * build(Container * container) override;
     I18n::Message name() override;
     I18n::Message upperName() override;
     const Image * icon() override;
   };
-  static Descriptor * buildDescriptor();
+  class Snapshot : public ::App::Snapshot {
+  public:
+    App * unpack(Container * container) override;
+    void reset() override;
+    Descriptor * descriptor() override;
+    Store * store();
+  private:
+    Store m_store;
+  };
 private:
-  App(Container * container, Descriptor * descriptor);
-  Store m_store;
+  App(Container * container, Snapshot * snapshot);
   CalculationController m_calculationController;
   AlternateEmptyViewController m_calculationAlternateEmptyViewController;
   ButtonRowController m_calculationHeader;
diff --git a/apps/sequence/app.cpp b/apps/sequence/app.cpp
index b5c964796..12d01680c 100644
--- a/apps/sequence/app.cpp
+++ b/apps/sequence/app.cpp
@@ -6,10 +6,6 @@ using namespace Poincare;
 
 namespace Sequence {
 
-App * App::Descriptor::build(Container * container) {
-  return new App(container, this);
-}
-
 I18n::Message App::Descriptor::name() {
   return I18n::Message::SequenceApp;
 }
@@ -22,19 +18,39 @@ const Image * App::Descriptor::icon() {
   return ImageStore::SequenceIcon;
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  FunctionApp(container, &m_inputViewController, descriptor),
-  m_sequenceStore(),
+App * App::Snapshot::unpack(Container * container) {
+  return new App(container, this);
+}
+
+void App::Snapshot::reset() {
+  m_sequenceStore.removeAll();
+}
+
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+SequenceStore * App::Snapshot::sequenceStore() {
+  return &m_sequenceStore;
+}
+
+void App::Snapshot::tidy() {
+  m_sequenceStore.tidy();
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  FunctionApp(container, snapshot, &m_inputViewController),
   m_nContext(((AppsContainer *)container)->globalContext()),
-  m_listController(&m_listFooter, &m_sequenceStore, &m_listHeader, &m_listFooter),
+  m_listController(&m_listFooter, snapshot->sequenceStore(), &m_listHeader, &m_listFooter),
   m_listFooter(&m_listHeader, &m_listController, &m_listController, ButtonRowController::Position::Bottom, ButtonRowController::Style::EmbossedGrey),
   m_listHeader(nullptr, &m_listFooter, &m_listController),
   m_listStackViewController(&m_tabViewController, &m_listHeader),
-  m_graphController(&m_graphAlternateEmptyViewController, &m_sequenceStore, &m_graphHeader),
+  m_graphController(&m_graphAlternateEmptyViewController, snapshot->sequenceStore(), &m_graphHeader),
   m_graphAlternateEmptyViewController(&m_graphHeader, &m_graphController, &m_graphController),
   m_graphHeader(&m_graphStackViewController, &m_graphAlternateEmptyViewController, &m_graphController),
   m_graphStackViewController(&m_tabViewController, &m_graphHeader),
-  m_valuesController(&m_valuesAlternateEmptyViewController, &m_sequenceStore, &m_valuesHeader),
+  m_valuesController(&m_valuesAlternateEmptyViewController, snapshot->sequenceStore(), &m_valuesHeader),
   m_valuesAlternateEmptyViewController(&m_valuesHeader, &m_valuesController, &m_valuesController),
   m_valuesHeader(nullptr, &m_valuesAlternateEmptyViewController, &m_valuesController),
   m_valuesStackViewController(&m_tabViewController, &m_valuesHeader),
@@ -43,10 +59,6 @@ App::App(Container * container, Descriptor * descriptor) :
 {
 }
 
-App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
-}
-
 InputViewController * App::inputViewController() {
   return &m_inputViewController;
 }
diff --git a/apps/sequence/app.h b/apps/sequence/app.h
index 8ad0d6ca1..b959fd82b 100644
--- a/apps/sequence/app.h
+++ b/apps/sequence/app.h
@@ -16,18 +16,25 @@ class App : public Shared::FunctionApp {
 public:
   class Descriptor : public ::App::Descriptor {
   public:
-    App * build(Container * container) override;
     I18n::Message name() override;
     I18n::Message upperName() override;
     const Image * icon() override;
   };
-  static Descriptor * buildDescriptor();
+  class Snapshot : public ::App::Snapshot {
+  public:
+    App * unpack(Container * container) override;
+    void reset() override;
+    Descriptor * descriptor() override;
+    SequenceStore * sequenceStore();
+  private:
+    void tidy() override;
+    SequenceStore m_sequenceStore;
+  };
   InputViewController * inputViewController() override;
   Poincare::Context * localContext() override;
   const char * XNT() override;
 private:
-  App(Container * container, Descriptor * descriptor);
-  SequenceStore m_sequenceStore;
+  App(Container * container, Snapshot * snapshot);
   LocalContext m_nContext;
   ListController m_listController;
   ButtonRowController m_listFooter;
diff --git a/apps/sequence/sequence.cpp b/apps/sequence/sequence.cpp
index b9951ca58..1a45135de 100644
--- a/apps/sequence/sequence.cpp
+++ b/apps/sequence/sequence.cpp
@@ -95,56 +95,40 @@ Sequence::Type Sequence::type() {
 
 void Sequence::setType(Type type) {
   m_type = type;
-  if (m_nameLayout != nullptr) {
-    delete m_nameLayout;
-    m_nameLayout = nullptr;
-  }
-  if (m_definitionName != nullptr) {
-    delete m_definitionName;
-    m_definitionName = nullptr;
-  }
-  if (m_firstInitialConditionName != nullptr) {
-    delete m_firstInitialConditionName;
-    m_firstInitialConditionName = nullptr;
-  }
-  if (m_secondInitialConditionName != nullptr) {
-    delete m_secondInitialConditionName;
-    m_secondInitialConditionName = nullptr;
-  }
+  tidy();
   /* Reset all contents */
   setContent("");
   setFirstInitialConditionContent("");
   setSecondInitialConditionContent("");
-  m_nameLayout = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("n", 1, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
-  if (m_type == Type::Explicite) {
-    m_definitionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("n ", 2, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
-  }
-  if (m_type == Type::SingleRecurrence) {
-    m_definitionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("n+1 ", 4, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
-    m_firstInitialConditionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("0", 1, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
-  }
-  if (m_type == Type::DoubleRecurrence) {
-    m_definitionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("n+2 ", 4, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
-    m_firstInitialConditionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("0", 1, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
-    m_secondInitialConditionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("1", 1, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
-  }
   m_indexBuffer[0] = -1;
   m_indexBuffer[1] = -1;
 }
 
 Poincare::Expression * Sequence::firstInitialConditionExpression() {
+  if (m_firstInitialConditionExpression == nullptr) {
+    m_firstInitialConditionExpression = Poincare::Expression::parse(m_firstInitialConditionText);
+  }
   return m_firstInitialConditionExpression;
 }
 
 Poincare::Expression * Sequence::secondInitialConditionExpression() {
+  if (m_secondInitialConditionExpression == nullptr) {
+    m_secondInitialConditionExpression = Poincare::Expression::parse(m_secondInitialConditionText);
+  }
   return m_secondInitialConditionExpression;
 }
 
 Poincare::ExpressionLayout * Sequence::firstInitialConditionLayout() {
+  if (m_firstInitialConditionLayout == nullptr && firstInitialConditionExpression() != nullptr) {
+    m_firstInitialConditionLayout = firstInitialConditionExpression()->createLayout(Expression::FloatDisplayMode::Decimal);
+  }
   return m_firstInitialConditionLayout;
 }
 
 Poincare::ExpressionLayout * Sequence::secondInitialConditionLayout() {
+  if (m_secondInitialConditionLayout == nullptr && secondInitialConditionExpression()) {
+    m_secondInitialConditionLayout = secondInitialConditionExpression()->createLayout(Expression::FloatDisplayMode::Decimal);
+  }
   return m_secondInitialConditionLayout;
 }
 
@@ -158,14 +142,11 @@ void Sequence::setFirstInitialConditionContent(const char * c) {
   strlcpy(m_firstInitialConditionText, c, sizeof(m_firstInitialConditionText));
   if (m_firstInitialConditionExpression != nullptr) {
     delete m_firstInitialConditionExpression;
+    m_firstInitialConditionExpression = nullptr;
   }
-  m_firstInitialConditionExpression = Poincare::Expression::parse(m_firstInitialConditionText);
   if (m_firstInitialConditionLayout != nullptr) {
     delete m_firstInitialConditionLayout;
-  }
-  m_firstInitialConditionLayout = nullptr;
-  if (m_firstInitialConditionExpression) {
-    m_firstInitialConditionLayout = m_firstInitialConditionExpression->createLayout(Expression::FloatDisplayMode::Decimal);
+    m_firstInitialConditionLayout = nullptr;
   }
   m_indexBuffer[0] = -1;
   m_indexBuffer[1] = -1;
@@ -175,14 +156,11 @@ void Sequence::setSecondInitialConditionContent(const char * c) {
   strlcpy(m_secondInitialConditionText, c, sizeof(m_secondInitialConditionText));
   if (m_secondInitialConditionExpression != nullptr) {
     delete m_secondInitialConditionExpression;
+    m_secondInitialConditionExpression = nullptr;
   }
-  m_secondInitialConditionExpression = Poincare::Expression::parse(m_secondInitialConditionText);
   if (m_secondInitialConditionLayout != nullptr) {
     delete m_secondInitialConditionLayout;
-  }
-  m_secondInitialConditionLayout = nullptr;
-  if (m_secondInitialConditionExpression) {
-    m_secondInitialConditionLayout = m_secondInitialConditionExpression->createLayout(Expression::FloatDisplayMode::Decimal);
+    m_secondInitialConditionLayout = nullptr;
   }
   m_indexBuffer[0] = -1;
   m_indexBuffer[1] = -1;
@@ -197,29 +175,57 @@ int Sequence::numberOfElements() {
 }
 
 Poincare::ExpressionLayout * Sequence::nameLayout() {
+  if (m_nameLayout == nullptr) {
+    m_nameLayout = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("n", 1, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
+  }
   return m_nameLayout;
 }
 
 Poincare::ExpressionLayout * Sequence::definitionName() {
+  if (m_definitionName == nullptr) {
+    if (m_type == Type::Explicite) {
+      m_definitionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("n ", 2, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
+    }
+    if (m_type == Type::SingleRecurrence) {
+      m_definitionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("n+1 ", 4, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
+    }
+    if (m_type == Type::DoubleRecurrence) {
+      m_definitionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("n+2 ", 4, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
+    }
+  }
   return m_definitionName;
 }
 
 Poincare::ExpressionLayout * Sequence::firstInitialConditionName() {
+  if (m_firstInitialConditionName == nullptr) {
+    if (m_type == Type::SingleRecurrence) {
+      m_firstInitialConditionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("0", 1, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
+    }
+    if (m_type == Type::DoubleRecurrence) {
+      m_firstInitialConditionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("0", 1, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
+    }
+  }
   return m_firstInitialConditionName;
 }
 
 Poincare::ExpressionLayout * Sequence::secondInitialConditionName() {
+  if (m_secondInitialConditionName == nullptr) {
+    if (m_type == Type::DoubleRecurrence) {
+      m_secondInitialConditionName = new BaselineRelativeLayout(new StringLayout(name(), 1), new StringLayout("1", 1, KDText::FontSize::Small), BaselineRelativeLayout::Type::Subscript);
+
+    }
+  }
   return m_secondInitialConditionName;
 }
 
 bool Sequence::isDefined() {
   switch (m_type) {
     case Type::Explicite:
-      return expression() != nullptr;
+      return strlen(text()) != 0;
     case Type::SingleRecurrence:
-      return expression() != nullptr && m_firstInitialConditionExpression != nullptr;
+      return strlen(text()) != 0 && strlen(firstInitialConditionText()) != 0;
     default:
-      return expression() != nullptr && m_firstInitialConditionExpression != nullptr && m_secondInitialConditionExpression != nullptr;
+      return strlen(text()) != 0 && strlen(firstInitialConditionText()) != 0 && strlen(secondInitialConditionText()) != 0;
   }
 }
 
@@ -319,4 +325,40 @@ float Sequence::sumOfTermsBetweenAbscissa(float start, float end, Context * cont
   return result;
 }
 
+void Sequence::tidy() {
+  Function::tidy();
+  if (m_firstInitialConditionLayout != nullptr) {
+    delete m_firstInitialConditionLayout;
+    m_firstInitialConditionLayout = nullptr;
+  }
+  if (m_secondInitialConditionLayout != nullptr) {
+    delete m_secondInitialConditionLayout;
+    m_secondInitialConditionLayout = nullptr;
+  }
+  if (m_firstInitialConditionExpression != nullptr) {
+    delete m_firstInitialConditionExpression;
+    m_firstInitialConditionExpression = nullptr;
+  }
+  if (m_secondInitialConditionExpression != nullptr) {
+    delete m_secondInitialConditionExpression;
+    m_secondInitialConditionExpression = nullptr;
+  }
+  if (m_nameLayout != nullptr) {
+    delete m_nameLayout;
+    m_nameLayout = nullptr;
+  }
+  if (m_definitionName != nullptr) {
+    delete m_definitionName;
+    m_definitionName = nullptr;
+  }
+  if (m_firstInitialConditionName != nullptr) {
+    delete m_firstInitialConditionName;
+    m_firstInitialConditionName = nullptr;
+  }
+  if (m_secondInitialConditionName != nullptr) {
+    delete m_secondInitialConditionName;
+    m_secondInitialConditionName = nullptr;
+  }
+}
+
 }
diff --git a/apps/sequence/sequence.h b/apps/sequence/sequence.h
index 6b39f836c..73a9f0991 100644
--- a/apps/sequence/sequence.h
+++ b/apps/sequence/sequence.h
@@ -38,6 +38,7 @@ public:
   bool isEmpty() override;
   float evaluateAtAbscissa(float x, Poincare::Context * context) const override;
   float sumOfTermsBetweenAbscissa(float start, float end, Poincare::Context * context);
+  void tidy() override;
 private:
   constexpr static int k_maxRecurrentRank = 10000;
   constexpr static float k_maxNumberOfTermsInSum = 100000.0f;
diff --git a/apps/settings/app.cpp b/apps/settings/app.cpp
index b68f28124..137768557 100644
--- a/apps/settings/app.cpp
+++ b/apps/settings/app.cpp
@@ -4,10 +4,6 @@
 
 namespace Settings {
 
-App * App::Descriptor::build(Container * container) {
-  return new App(container, this);
-}
-
 I18n::Message App::Descriptor::name() {
   return I18n::Message::SettingsApp;
 }
@@ -20,15 +16,20 @@ const Image * App::Descriptor::icon() {
   return ImageStore::SettingsIcon;
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  ::App(container, &m_stackViewController, descriptor, I18n::Message::Warning),
+App * App::Snapshot::unpack(Container * container) {
+  return new App(container, this);
+}
+
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  ::App(container, snapshot, &m_stackViewController, I18n::Message::Warning),
   m_mainController(&m_stackViewController),
   m_stackViewController(&m_modalViewController, &m_mainController)
 {
 }
 
-App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
-}
-
 }
diff --git a/apps/settings/app.h b/apps/settings/app.h
index 6661a38e5..ea9170848 100644
--- a/apps/settings/app.h
+++ b/apps/settings/app.h
@@ -10,14 +10,17 @@ class App : public ::App {
 public:
   class Descriptor : public ::App::Descriptor {
   public:
-    App * build(Container * container) override;
     I18n::Message name() override;
     I18n::Message upperName() override;
     const Image * icon() override;
   };
-  static Descriptor * buildDescriptor();
+  class Snapshot : public ::App::Snapshot {
+  public:
+    App * unpack(Container * container) override;
+    Descriptor * descriptor() override;
+  };
 private:
-  App(Container * container, Descriptor * descriptor);
+  App(Container * container, Snapshot * snapshot);
   MainController m_mainController;
   StackViewController m_stackViewController;
 };
diff --git a/apps/settings/sub_controller.cpp b/apps/settings/sub_controller.cpp
index 9dea636cd..c6ba73d98 100644
--- a/apps/settings/sub_controller.cpp
+++ b/apps/settings/sub_controller.cpp
@@ -60,7 +60,7 @@ bool SubController::handleEvent(Ion::Events::Event event) {
    * clicking on '6' on the serial number row. */
   if (event == Ion::Events::Six && m_nodeModel->label() == I18n::Message::About && selectedRow() == 1) {
     AppsContainer * appsContainer = (AppsContainer *)app()->container();
-    appsContainer->switchTo(appsContainer->hardwareTestAppDescriptor());
+    appsContainer->switchTo(appsContainer->hardwareTestAppSnapshot());
     return true;
   }
   if (event == Ion::Events::OK || event == Ion::Events::EXE) {
diff --git a/apps/shared/function.cpp b/apps/shared/function.cpp
index e5251f83d..7cb2bb0fa 100644
--- a/apps/shared/function.cpp
+++ b/apps/shared/function.cpp
@@ -27,16 +27,13 @@ Function& Function::operator=(const Function& other) {
 
 void Function::setContent(const char * c) {
   strlcpy(m_text, c, sizeof(m_text));
-  if (m_expression != nullptr) {
-    delete m_expression;
-  }
-  m_expression = Poincare::Expression::parse(m_text);
   if (m_layout != nullptr) {
     delete m_layout;
+    m_layout = nullptr;
   }
-  m_layout = nullptr;
-  if (m_expression) {
-    m_layout = expression()->createLayout(Expression::FloatDisplayMode::Decimal);
+  if (m_expression != nullptr) {
+    delete m_expression;
+    m_expression = nullptr;
   }
 }
 
@@ -64,15 +61,21 @@ const char * Function::name() const {
 }
 
 Poincare::Expression * Function::expression() {
+  if (m_expression == nullptr) {
+    m_expression = Expression::parse(m_text);
+  }
   return m_expression;
 }
 
 Poincare::ExpressionLayout * Function::layout() {
+  if (m_layout == nullptr && expression() != nullptr) {
+    m_layout = expression()->createLayout(Expression::FloatDisplayMode::Decimal);
+  }
   return m_layout;
 }
 
 bool Function::isDefined() {
-  return m_expression != nullptr;
+  return strlen(m_text) != 0;
 }
 
 bool Function::isActive() {
@@ -95,4 +98,15 @@ float Function::evaluateAtAbscissa(float x, Poincare::Context * context) const {
   return m_expression->approximate(variableContext);
 }
 
+void Function::tidy() {
+  if (m_layout != nullptr) {
+    delete m_layout;
+    m_layout = nullptr;
+  }
+  if (m_expression != nullptr) {
+    delete m_expression;
+    m_expression = nullptr;
+  }
+}
+
 }
diff --git a/apps/shared/function.h b/apps/shared/function.h
index 67abb12b0..b3e0b05a5 100644
--- a/apps/shared/function.h
+++ b/apps/shared/function.h
@@ -27,6 +27,7 @@ public:
   virtual void setContent(const char * c);
   void setColor(KDColor m_color);
   virtual float evaluateAtAbscissa(float x, Poincare::Context * context) const;
+  virtual void tidy();
 protected:
   Poincare::Expression * m_expression;
 private:
diff --git a/apps/shared/function_app.cpp b/apps/shared/function_app.cpp
index d15392b64..3804c4110 100644
--- a/apps/shared/function_app.cpp
+++ b/apps/shared/function_app.cpp
@@ -5,8 +5,8 @@ using namespace Poincare;
 
 namespace Shared {
 
-FunctionApp::FunctionApp(Container * container, ViewController * rootViewController, Descriptor * descriptor) :
-  TextFieldDelegateApp(container, rootViewController, descriptor)
+FunctionApp::FunctionApp(Container * container, Snapshot * snapshot, ViewController * rootViewController) :
+  TextFieldDelegateApp(container, snapshot, rootViewController)
 {
 }
 
diff --git a/apps/shared/function_app.h b/apps/shared/function_app.h
index 575663b74..5c592e8bc 100644
--- a/apps/shared/function_app.h
+++ b/apps/shared/function_app.h
@@ -10,7 +10,8 @@ namespace Shared {
 
 class FunctionApp : public TextFieldDelegateApp {
 public:
-  FunctionApp(Container * container, ViewController * rootViewController, Descriptor * descriptor);
+  FunctionApp(Container * container, Snapshot * snapshot, ViewController * rootViewController);
+  virtual ~FunctionApp() = default;
   virtual InputViewController * inputViewController() = 0;
   void willBecomeInactive() override;
 };
diff --git a/apps/shared/function_store.cpp b/apps/shared/function_store.cpp
index 0c735f7aa..a5102db74 100644
--- a/apps/shared/function_store.cpp
+++ b/apps/shared/function_store.cpp
@@ -62,4 +62,10 @@ int FunctionStore::numberOfDefinedFunctions() {
   return result;
 }
 
+void FunctionStore::tidy() {
+  for (int i = 0; i < m_numberOfFunctions; i++) {
+    functionAtIndex(i)->tidy();
+  }
+}
+
 }
diff --git a/apps/shared/function_store.h b/apps/shared/function_store.h
index b8d8272ae..93d1c2397 100644
--- a/apps/shared/function_store.h
+++ b/apps/shared/function_store.h
@@ -26,6 +26,7 @@ public:
   int numberOfActiveFunctions();
   virtual int maxNumberOfFunctions() = 0;
   virtual char symbol() const = 0;
+  void tidy();
 protected:
   int m_numberOfFunctions;
 private:
diff --git a/apps/shared/text_field_delegate_app.cpp b/apps/shared/text_field_delegate_app.cpp
index 628419c69..22ae44e3a 100644
--- a/apps/shared/text_field_delegate_app.cpp
+++ b/apps/shared/text_field_delegate_app.cpp
@@ -7,8 +7,8 @@ using namespace Poincare;
 
 namespace Shared {
 
-TextFieldDelegateApp::TextFieldDelegateApp(Container * container, ViewController * rootViewController, Descriptor * descriptor) :
-  ::App(container, rootViewController, descriptor, I18n::Message::Warning),
+TextFieldDelegateApp::TextFieldDelegateApp(Container * container, Snapshot * snapshot, ViewController * rootViewController) :
+  ::App(container, snapshot, rootViewController, I18n::Message::Warning),
   TextFieldDelegate()
 {
 }
diff --git a/apps/shared/text_field_delegate_app.h b/apps/shared/text_field_delegate_app.h
index 29c41d7d2..9d3d95573 100644
--- a/apps/shared/text_field_delegate_app.h
+++ b/apps/shared/text_field_delegate_app.h
@@ -11,7 +11,8 @@ namespace Shared {
 
 class TextFieldDelegateApp : public ::App, public TextFieldDelegate {
 public:
-  TextFieldDelegateApp(Container * container, ViewController * rootViewController, Descriptor * descriptor);
+  TextFieldDelegateApp(Container * container, Snapshot * snapshot, ViewController * rootViewController);
+  virtual ~TextFieldDelegateApp() = default;
   virtual Poincare::Context * localContext();
   AppsContainer * container();
   virtual const char * XNT();
diff --git a/apps/statistics/app.cpp b/apps/statistics/app.cpp
index f65290228..cea063eaf 100644
--- a/apps/statistics/app.cpp
+++ b/apps/statistics/app.cpp
@@ -1,14 +1,11 @@
 #include "app.h"
 #include "stat_icon.h"
+#include "../i18n.h"
 
 using namespace Shared;
 
 namespace Statistics {
 
-App * App::Descriptor::build(Container * container) {
-  return new App(container, this);
-}
-
 I18n::Message App::Descriptor::name() {
   return I18n::Message::StatsApp;
 }
@@ -21,28 +18,40 @@ const Image * App::Descriptor::icon() {
   return ImageStore::StatIcon;
 }
 
-App::App(Container * container, Descriptor * descriptor) :
-  TextFieldDelegateApp(container, &m_tabViewController, descriptor),
-  m_store(),
-  m_calculationController(&m_calculationAlternateEmptyViewController, &m_calculationHeader, &m_store),
+App * App::Snapshot::unpack(Container * container) {
+  return new App(container, this);
+}
+
+void App::Snapshot::reset() {
+  m_store.deleteAllPairs();
+}
+
+App::Descriptor * App::Snapshot::descriptor() {
+  static Descriptor descriptor;
+  return &descriptor;
+}
+
+Store * App::Snapshot::store() {
+  return &m_store;
+}
+
+App::App(Container * container, Snapshot * snapshot) :
+  TextFieldDelegateApp(container, snapshot, &m_tabViewController),
+  m_calculationController(&m_calculationAlternateEmptyViewController, &m_calculationHeader, snapshot->store()),
   m_calculationAlternateEmptyViewController(&m_calculationHeader, &m_calculationController, &m_calculationController),
   m_calculationHeader(&m_tabViewController, &m_calculationAlternateEmptyViewController, &m_calculationController),
-  m_boxController(&m_boxAlternateEmptyViewController, &m_boxHeader, &m_store),
+  m_boxController(&m_boxAlternateEmptyViewController, &m_boxHeader, snapshot->store()),
   m_boxAlternateEmptyViewController(&m_boxHeader, &m_boxController, &m_boxController),
   m_boxHeader(&m_tabViewController, &m_boxAlternateEmptyViewController, &m_boxController),
-  m_histogramController(&m_histogramAlternateEmptyViewController, &m_histogramHeader, &m_store),
+  m_histogramController(&m_histogramAlternateEmptyViewController, &m_histogramHeader, snapshot->store()),
   m_histogramAlternateEmptyViewController(&m_histogramHeader, &m_histogramController, &m_histogramController),
   m_histogramHeader(&m_histogramStackViewController, &m_histogramAlternateEmptyViewController, &m_histogramController),
   m_histogramStackViewController(&m_tabViewController, &m_histogramHeader),
-  m_storeController(&m_storeHeader, &m_store, &m_storeHeader),
+  m_storeController(&m_storeHeader, snapshot->store(), &m_storeHeader),
   m_storeHeader(&m_storeStackViewController, &m_storeController, &m_storeController),
   m_storeStackViewController(&m_tabViewController, &m_storeHeader),
-  m_tabViewController(&m_modalViewController, &m_storeStackViewController, &m_histogramStackViewController, &m_boxHeader, &m_calculationHeader)
+   m_tabViewController(&m_modalViewController, &m_storeStackViewController, &m_histogramStackViewController, &m_boxHeader, &m_calculationHeader)
 {
 }
 
-App::Descriptor * App::buildDescriptor() {
-  return new App::Descriptor();
-}
-
 }
diff --git a/apps/statistics/app.h b/apps/statistics/app.h
index 56c4699a9..7016887a8 100644
--- a/apps/statistics/app.h
+++ b/apps/statistics/app.h
@@ -15,15 +15,21 @@ class App : public Shared::TextFieldDelegateApp {
 public:
   class Descriptor : public ::App::Descriptor {
   public:
-    App * build(Container * container) override;
     I18n::Message name() override;
     I18n::Message upperName() override;
     const Image * icon() override;
   };
-  static Descriptor * buildDescriptor();
+  class Snapshot : public ::App::Snapshot {
+  public:
+    App * unpack(Container * container) override;
+    void reset() override;
+    Descriptor * descriptor() override;
+    Store * store();
+  private:
+    Store m_store;
+  };
 private:
-  App(Container * container, Descriptor * descriptor);
-  Store m_store;
+  App(Container * container, Snapshot * snapshot);
   CalculationController m_calculationController;
   AlternateEmptyViewController m_calculationAlternateEmptyViewController;
   ButtonRowController m_calculationHeader;
diff --git a/escher/include/escher/app.h b/escher/include/escher/app.h
index 792ab6ed8..8bbc8b60a 100644
--- a/escher/include/escher/app.h
+++ b/escher/include/escher/app.h
@@ -23,16 +23,24 @@ class App : public Responder {
 public:
   class Descriptor {
   public:
-    virtual App * build(Container * container) = 0;
     virtual I18n::Message name();
     virtual I18n::Message upperName();
     virtual const Image * icon();
   };
-  /* Each App subclass must implement
-   * static Descriptor * builDescriptor(); */
-  Descriptor * descriptor();
+  class Snapshot {
+  public:
+    virtual App * unpack(Container * container) = 0;
+    void pack(App * app);
+    /* reset all instances to their initial values */
+    virtual void reset();
+    virtual Descriptor * descriptor() = 0;
+  private:
+    /* tidy clean all dynamically-allocated data */
+    virtual void tidy();
+  };
   virtual ~App() = default;
   constexpr static uint8_t Magic = 0xA8;
+  Snapshot * snapshot();
   void setFirstResponder(Responder * responder);
   Responder * firstResponder();
   bool processEvent(Ion::Events::Event event);
@@ -46,12 +54,12 @@ public:
   virtual void didBecomeActive(Window * window);
   virtual void willBecomeInactive();
 protected:
-  App(Container * container, ViewController * rootViewController, Descriptor * descriptor, I18n::Message warningMessage = (I18n::Message)0);
+  App(Container * container, Snapshot * snapshot, ViewController * rootViewController, I18n::Message warningMessage = (I18n::Message)0);
   ModalViewController m_modalViewController;
 private:
-  Descriptor * m_descriptor;
   Container * m_container;
   Responder * m_firstResponder;
+  Snapshot * m_snapshot;
   WarningController m_warningController;
 };
 
diff --git a/escher/include/escher/container.h b/escher/include/escher/container.h
index 78343454c..8412274ff 100644
--- a/escher/include/escher/container.h
+++ b/escher/include/escher/container.h
@@ -26,7 +26,7 @@ public:
   void run();
   App * activeApp();
   virtual bool dispatchEvent(Ion::Events::Event event) override;
-  virtual void switchTo(App::Descriptor * descriptor);
+  virtual void switchTo(App::Snapshot * snapshot);
 protected:
   virtual Window * window() = 0;
   void windowRedraw() override;
diff --git a/escher/src/app.cpp b/escher/src/app.cpp
index b3bf406a7..4893ae0c4 100644
--- a/escher/src/app.cpp
+++ b/escher/src/app.cpp
@@ -16,19 +16,30 @@ const Image * App::Descriptor::icon() {
   return nullptr;
 }
 
-App::App(Container * container, ViewController * rootViewController, Descriptor * descriptor, I18n::Message warningMessage) :
+void App::Snapshot::pack(App * app) {
+  tidy();
+  delete app;
+}
+
+void App::Snapshot::reset() {
+}
+
+void App::Snapshot::tidy() {
+}
+
+App::App(Container * container, Snapshot * snapshot, ViewController * rootViewController, I18n::Message warningMessage) :
   Responder(nullptr),
   m_magic(Magic),
   m_modalViewController(this, rootViewController),
-  m_descriptor(descriptor),
   m_container(container),
   m_firstResponder(nullptr),
+  m_snapshot(snapshot),
   m_warningController(this, warningMessage)
 {
 }
 
-App::Descriptor * App::descriptor() {
-  return m_descriptor;
+App::Snapshot * App::snapshot() {
+  return m_snapshot;
 }
 
 bool App::processEvent(Ion::Events::Event event) {
diff --git a/escher/src/container.cpp b/escher/src/container.cpp
index cd7c273c1..2314eda06 100644
--- a/escher/src/container.cpp
+++ b/escher/src/container.cpp
@@ -13,13 +13,18 @@ Container::~Container() {
   }
 }
 
-void Container::switchTo(App::Descriptor * descriptor) {
+void Container::switchTo(App::Snapshot * snapshot) {
+  if (m_activeApp && snapshot == m_activeApp->snapshot()) {
+    return;
+  }
   if (m_activeApp) {
     m_activeApp->willBecomeInactive();
-    delete m_activeApp;
+    m_activeApp->snapshot()->pack(m_activeApp);
   }
-  if (descriptor) {
-    m_activeApp = descriptor->build(this);
+  if (snapshot) {
+    m_activeApp = snapshot->unpack(this);
+  } else {
+    m_activeApp = nullptr;
   }
   if (m_activeApp) {
     m_activeApp->didBecomeActive(window());