diff --git a/poincare/src/zoom.cpp b/poincare/src/zoom.cpp
index 3ebdfe412..b999a4d17 100644
--- a/poincare/src/zoom.cpp
+++ b/poincare/src/zoom.cpp
@@ -247,6 +247,12 @@ void Zoom::RefinedYRangeForDisplay(ValueAtAbscissa evaluation, float xMin, float
 }
 
 void Zoom::RangeWithRatioForDisplay(ValueAtAbscissa evaluation, float yxRatio, float * xMin, float * xMax, float * yMin, float * yMax, Context * context, const void * auxiliary) {
+  /* The goal of this algorithm is to find the window with given ratio, that
+   * best suits the function.
+   * - The X range is centered around a point of interest of the function, or
+   *   0 if none exist, and uses a default width of 20.
+   * - The Y range's height is fixed at 20*yxRatio. Its center is chosen to
+   *   maximize the number of visible points of the function. */
   constexpr float minimalXCoverage = 0.15f;
   constexpr float minimalYCoverage = 0.3f;
   constexpr int sampleSize = k_sampleSize * 2;
@@ -274,6 +280,18 @@ void Zoom::RangeWithRatioForDisplay(ValueAtAbscissa evaluation, float yxRatio, f
       sample,
       sampleSize);
 
+  /* For each value taken by the sample of the function on [xMin, xMax], given
+   * a fixed value for yRange, we measure the number (referred to as breadth)
+   * of other points that could be displayed if this value was chosen as yMin.
+   * In other terms, given a sorted set Y={y1,...,yn} and a length dy, we look
+   * for the pair 1<=i,j<=n such that :
+   *   - yj - yi <= dy
+   *   - i - j is maximal
+   * The fact that the sample is sorted makes it possible to find i and j in
+   * linear time.
+   * In case of pairs having the same breadth, we chose the pair that minimizes
+   * the criteria distanceFromCenter, which makes the window symmetrical when
+   * dealing with linear functions. */
   float yRange = yxRatio * xRange;
   int j = 1;
   int bestIndex, bestBreadth = 0, bestDistanceToCenter;
@@ -295,6 +313,9 @@ void Zoom::RangeWithRatioForDisplay(ValueAtAbscissa evaluation, float yxRatio, f
     }
   }
 
+  /* Functions with a very steep slope might only take a small portion of the
+   * X axis. Conversely, very flat functions may only take a small portion of
+   * the Y range. In those cases, the ratio is not suitable. */
   if (bestBreadth < minimalXCoverage * sampleSize
    || sample[bestIndex + bestBreadth] - sample[bestIndex] < minimalYCoverage * yRange) {
     *xMin = NAN;