Suddenly, without my being aware of changing anything, the use of the
right-click and drag to measure distances has started to produce not
only the straight line, but also an accompanying dotted line that leaves
a trail after the measurement is done. Screen redraw is the only way to
remove it. If I move the mouse around during the drag process, a trail
of dots are 'sprayed' around the screen. Weird eh?

What did I do wrong?

Lawrence Harris