This is surprisingly accurate metronome.
Utilize for practicing instruments.

S4 Metronome is a surprisingly accurate metronome app.

Features:
-This app is programmed to control the time in 1/44100 second, meaning it is highly accurate.
-You can set a tempo by each 0.01bpm, from 20 bpm to 400 bpm.
-Even on mute, you can use this app by checking the visual beat simulation such as the motion of a ball and blinking indicator.
-Supports black or white background. Choose better one depends on your environment.
-Supports irregular beats.
-Four different sounds are available. (Click, Metronome, Clave, and DrumSet)
-It is simple to use, but highly-functional to satisfy professionals.

Note: You can save the settings only in the paid version.