Not bad but could be better No bugs  just missing an important feature. Pressing calibrate just zeros the level - poor! It should take a measurement  tell you to rotate 180 take another  then zero using the difference. If your phone is in a case it's the only way to get it right (same way levels have always been calibrated). I've never seen a phone with buttons on the back  and if you're using it on it's side you're not turning it over you're rotating it - calibration would compensate for the buttons. Stop making excuses and fix it.
August 24 2015