diff --git a/sohstationviewer/view/plotting/plotting_widget/plotting.py b/sohstationviewer/view/plotting/plotting_widget/plotting.py
index 44389d328c8fa6281338b0365b132c53710cd8a4..74ebf7f5d1bda1178ebcdcb577c38c1ac3e7c2b7 100644
--- a/sohstationviewer/view/plotting/plotting_widget/plotting.py
+++ b/sohstationviewer/view/plotting/plotting_widget/plotting.py
@@ -181,6 +181,8 @@ class Plotting:
             sample_no_pos=[0.25, 0.75],
             chan_db_info=chan_db_info, linked_ax=linked_ax)
 
+        # x_bottom, x_top are the times of data points to be displayed at
+        # bottom or top of the plot
         ax.x_bottom = np.array(points_list[0])
         ax.x_top = np.array(points_list[1])
 
diff --git a/sohstationviewer/view/plotting/plotting_widget/plotting_axes.py b/sohstationviewer/view/plotting/plotting_widget/plotting_axes.py
index 070cb236d537f3d42954c46c46e1bf913ff17620..cbe97d14472c1054915a2e7f9f9f32b1ab4a0d11 100644
--- a/sohstationviewer/view/plotting/plotting_widget/plotting_axes.py
+++ b/sohstationviewer/view/plotting/plotting_widget/plotting_axes.py
@@ -222,6 +222,10 @@ class PlottingAxes:
 
         # set samples' total on right side
         if len(sample_no_list) == 1:
+            # center_total_point_lbl: The label to display total number of data
+            # points for plots whose ax has attribute x_list.
+            # The plotTypes that use this label are linesDot, linesSRate,
+            # linesMassPos, dotForTime, multiColorDot
             ax.center_total_point_lbl = ax.text(
                 1.005, 0.5,
                 sample_no_list[0],
@@ -233,13 +237,12 @@ class PlottingAxes:
                 size=self.parent.font_size
             )
         else:
-            # Each zoom this infor is created again.
-            # Plots that have data separated in two to have text in top and
-            # bottom, sample rate= 1. These numbers completely depends
-            # on data created in trim_downsample_chan_with_spr_less_or_equal_1
-            # and won't be changed in set_lim, then don't need to assign a
-            # variable for it.
-            # bottom
+            # bottom_total_point_lbl, top_total_point_lbl are label to diplay
+            # total number of data points which are splitted into top
+            # and bottom. The ax needs to include attributes x_bottom and x_top
+            # The plotTypes that use these labels are upDownDots (and linesDot
+            # with channel='GPS Lk/Unlk' which will have another MR to add
+            # x_bottom and x_top for this)
             ax.bottom_total_point_lbl = ax.text(
                 1.005, sample_no_pos[0],
                 sample_no_list[0],