This app is a very simple way to estimate something or someone's speed if you can position yourself to see when that person/thing goes by 2 points that you know the distance between. This is also known as a “tachymeter” which means "facility on a watch for measuring speed”. (by the way, Apple Watch owners have all this app’s features right on their wrist).

The distance units include feet, meters, miles, km, and yards while the speed units include mph, km/h, ft/s, m/s, and knots. Switching between these units is done right on the main screen with a simple picker that does the conversions on the fly as you turn the pickers’ wheels on the iPhone while the Apple Watch version has an options screen and numpad to enter the distance.

This app simply does the timing and math, including the conversions for you. You could do the same thing with a timer and calculator (or even google instead of the calculator) but this makes it a lot easier, quicker and all on one screen.

If you were to use this at the start and end of a racer's race or lap, of course it would give you the racer's average speed so this app could be useful at different types of races. It could also be used between shorter known distances for more of an "instant read".