To make the joke press volume key while scanning and result size will be big.
To begin the analysis place the finger on the fingerprint and after the scanning you will show the result penis size.
To make the prank to your friends press the volume up or down button while scanning your finger, and the result size will be big. Then, when you let your friend try, it will always be small.
This application is a joke and the measure is not real, it will be as accurate as great is your sense of humor.