Measuring Reaction Time

A simple device for measuring reaction time is made of a strip of cardboard, marked with a scale and two large dots, one at the top and one at the bottom. Your friend holds the strip with his thumb and forefinger at the upper dot, and you position your thumb and forefinger at the lower dot, being careful not to touch the strip. Your friend releases the strip, and you try to pinch it as soon as possible after you see it begin to fall. The mark at the place where you pinch the strip gives your reaction time. How far from the lower dot should you place the 50-, 100-, 200- and 250-ms marks?