Define Harvard Step Test - aerobic capacity?

In this test, the subject steps on and off an 18-inch platform at a rate of 30 times per minute. The evaluator records the subject's pulse rate at 30 seconds, 1 minute, 2 minutes, and 3 minutes after the exercise. The following formula is then applied:

Physical Efficiency Index (PIE) = Duration of exercise in seconds x 100 / 2 x sums of any 3 pulse counts during recovery

The higher the index better is the person's status. There are many variations to this test and is easy to perform. Used as a field method, it gives an idea of aerobic fitness of the subject.