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Passion works by using all of the iPhone's distinct features such as the microphone, accelerometer and many others to determine an accurate score. All you have to do is start the application, put your iPhone on the bed, in an arm band, or even in your pocket and have intercourse, it is as easy as that. Once you are finished, press the stop button and view your results.

http://gizmodo.com/5323832/passion-iphone-app-will-let-you-see-how-good-you-are-at-sex