The vertical jump is a measurement, like the 40 yd dash, that must be taken with a grain of salt. The standard measurement is taken by standing flat footed and jumping, but these days with so much riding on the "measureables", guys cheat. I have seen coaches measure VJ with one step, then jump, two steps, etc. I believe Michael Jordan was credited with a 42 inch vertical, but the rumor is that he took multiple steps to get that measurement.