Show time label on top of ruler

Closes #71 (closed)

sohstationviewer/view/plotting/plotting_widget/plotting_widget.py

@@ -203,9 +203,15 @@ class PlottingWidget(QtWidgets.QScrollArea):
         """
         self.plotting = Plotting(self, self.plotting_axes,
                                  parent_params=parent)
-
+        """
+        new_min_x: store the new minimum time for zooming; used to fix a
+        problem where after the first zoom marker is chosen, any ruler that is
+        to the left of the first zoom marker does not have text above it.
+        """
         self.new_min_x = float('-inf')
-
+        """
+        ruler_text: the current text shown above the ruler
+        """
         self.ruler_text: Optional[matplotlib.text.Text] = None
 
         self.set_colors('B')
@@ -351,6 +357,13 @@ class PlottingWidget(QtWidgets.QScrollArea):
                 pass
 
         for w in self.peer_plotting_widgets:
+            if modifiers in [QtCore.Qt.ControlModifier, QtCore.Qt.MetaModifier,
+                             Qt.ShiftModifier]:
+                try:
+                    w.ruler_text.remove()
+                    w.ruler_text = None
+                except AttributeError:
+                    pass
             if modifiers == QtCore.Qt.ShiftModifier:
                 w.on_shift_click(xdata)
             elif modifiers in [QtCore.Qt.ControlModifier,