diff --git a/apps/regression/graph_controller.h b/apps/regression/graph_controller.h
index 49bc1076e..48a162873 100644
--- a/apps/regression/graph_controller.h
+++ b/apps/regression/graph_controller.h
@@ -44,6 +44,7 @@ private:
   void initCursorParameters() override;
   uint32_t modelVersion() override;
   uint32_t rangeVersion() override;
+  int selectedCurveIndex() const override { return *m_selectedSeriesIndex; }
   bool closestCurveIndexIsSuitable(int newIndex, int currentIndex) const override;
   double yValue(int curveIndex, double x, Poincare::Context * context) const override;
   bool suitableYValue(double y) const override;
diff --git a/apps/shared/function_graph_controller.h b/apps/shared/function_graph_controller.h
index bf43ca2df..ac7114ff2 100644
--- a/apps/shared/function_graph_controller.h
+++ b/apps/shared/function_graph_controller.h
@@ -40,6 +40,7 @@ private:
   CurveView * curveView() override;
   uint32_t modelVersion() override;
   uint32_t rangeVersion() override;
+  int selectedCurveIndex() const override { return *m_indexFunctionSelectedByCursor; }
   bool closestCurveIndexIsSuitable(int newIndex, int currentIndex) const override;
   double yValue(int curveIndex, double x, Poincare::Context * context) const override;
   int numberOfCurves() const override;
diff --git a/apps/shared/interactive_curve_view_controller.h b/apps/shared/interactive_curve_view_controller.h
index 6ff234718..08a2e34ad 100644
--- a/apps/shared/interactive_curve_view_controller.h
+++ b/apps/shared/interactive_curve_view_controller.h
@@ -40,8 +40,9 @@ protected:
 
   // Closest vertical curve helper
   int closestCurveIndexVertically(bool goingUp, int currentSelectedCurve, Poincare::Context * context) const;
-  virtual bool closestCurveIndexIsSuitable(int newIndex, int currentIndex) const { assert(false); return false; }
-  virtual double yValue(int curveIndex, double x, Poincare::Context * context) const { assert(false); return 0; }
+  virtual bool closestCurveIndexIsSuitable(int newIndex, int currentIndex) const = 0;
+  virtual int selectedCurveIndex() const = 0;
+  virtual double yValue(int curveIndex, double x, Poincare::Context * context) const = 0;
   virtual bool suitableYValue(double y) const { return true; }
   virtual int numberOfCurves() const = 0;