A must have app for BASE jumpers, Rockdrop Pro makes measuring height of vertical cliffs easier and more precise. Instead of tapping a button to start and stop the stopwatch (which can be difficult to do precisely and prone to accidental touches when throwing a rock), you simply press the screen anywhere and release it simultaneously with the rock, then press it again anytime while the rock is falling and release on rock impact. Easy, simple, precise. No looking at the screen necessary, no accidental touches. The app also automatically compensates for sound delay if you detect the impact by sound - an important correction many jumpers neglect.
The calculations are based on Wingsuit Equations with the standard sustained fall rate of 120mph. Since the exact sustained fall rate of any particular rock is not known, the calculated height can be different from laser measurements and actual height. Light, flaky rocks have lower sustained fall rate and thus produce overestimated height. Always remember that it's better to underestimate height than overestimate it.