Here are two verticle lines of identical length. One has reversed arrowheads while the other's look normal. One of the lines looks longer!
     Something about the arrowheads are distorting our perception. It may be our "built-in" sense of perspective.
     Adjust the blue line on the left by pulling the top, or bottom end. When both lines appear to be the same length,
     Press show measure.
     Press reset to equalize line lengths