This app measures the lap and the swimming distance by detecting flip turn sound.
It starts a timer after 5 second beep sound countdown when you press the start button.
It waits for the sound of the turn 5 seconds before and after the expected lap time. The initial value of expected lap is 45 seconds. You can change it on the screen. The expected lap will be updated system-internally at each turn, so it can be measured correctly unless the pace suddenly changes.
The method of detecting the sound of the turn is when the loudest sound is detected in 10 seconds. It's so simple. So it can not be measured correctly when used in noisy places or when swimming with multiple people.