A goniometer is a tool used to measure the range of motion of various joints around the body. It is usually a plastic transparent ruler type, but in the age of new technology, you can use your phone to get a similar reading.
It is possible to use the accelerometer chip in your mobile device to calculate the angle of rotation, much like a digital gravity inclinometer. This is a handy app for those working in the health professional field who need a quick and simple range of motion measure.
Find it on the USA App Store: Goniometer App - by June Gaming
To measure the range of motion using this app, all you need to do is "set 0º" to establish a relative 0º, then rotate the device to desired angle and "get reading". Simple as that.