Shift Controls

The four buttons appearing below the Reset Shift button all change the
data translation when they are held down:

up arrow      shift the plot upward
down arrow    shift the plot downward

right arrow   shift the plot to the right
left arrow    shift the plot to the left

In addition, the shift can be adjusted by dragging left inside the
plotting window. This allows the user to grab the point cloud and move
it around the plotting window synchronously with the cursor.