I calculated the airspeed of a rubber band this way once! My coworker shot a rubber band in my direction. I noticed three “shadows” of the rubber band as it pas

I calculated the airspeed of a rubber band this way once! My coworker shot a rubber band in my direction. I noticed three “shadows” of the rubber band as it passed by the CRT. The CRT was a 17” running at 60hz. The rubber band sailed past in the span of about 2 screen refreshes, so it traveled that distance in 2/60 of a second. Distance was easy to calculate by the Pythagorean theorem or by holding a ruler to the screen, I forget which.