Wouldn't work. A lot of users use headphones. I like your angle though. You would be better off asking the use to throw their iPad up in the air (at least 3 me

Wouldn't work. A lot of users use headphones. I like your angle though. You would be better off asking the use to throw their iPad up in the air (at least 3 metres for accuracy) and measure the time it takes to come to rest. Just remember to use the microphone to listen for a cracking of glass sound so the algorithm is correct.