The app fulfills its purpose in a very (too much?) simple interface. It misses a mute sound/flashing blink feature. Surprisingly, it has a very sophisticated tuning aid feature, with even two different microtonal tuning systems, but lacks other pitch references than the north-american A440 (you can do that using the Lucy system, though), and has no other choice but the A as reference. But from the bunch of metronome apps I downloaded to try, seemed me the best one.