With SprintTimer I claim that the accuracy is almost as good as a high end professional fully automatic timing equipment. This article presents some measurement I made to test this claim. Since the most accurate method to measure a race is to start the clock with a sound and the finish with Photo Finish, I have focused on that setup, but also tested some other variations.
All iPhone and iPad cameras have fairly wide angle lenses. This means that you must stand pretty close to the participants to fill out the image when recording a Photo or Video Finish. Sometimes this is an advantage (e.g. indoors), but in most cases, it is the opposite. In many water sports like rowing and kayaking, it can be difficult to get close to the finish line. And if the participants have different lanes, like in a 100 m sprint, standing close makes it impossible to set a slice width that fits all runners. This because the runners move with very different speed as seen by the camera.