Photo Ruler is designed to accurately determine the size of any object by either taking a picture of it or measuring it on the screen. With its simple user-friendly design Photo Ruler allows you to measure things just as conveniently and precisely as with a traditional ruler or tape measure. ALSO AVAILABLE FOR IPHONE: https://itunes. apple.com/us/app/photo-ruler-measure-and-label/id1020133524? mt=8How to use:Method 1:Firstly, please ensure that the object you wish to measure and the object of known length (Base Item) are in the same picture. Double tap on screen to call settings. There is a predefined list of Base Items, including Debit/credit card and Quarter. Select the one you have. It is advised to use the Base Item which is closest in size to the object you wish to measure. Secondly, ensure that the Base Item and the object you wish to measure are in the same plane and the camera is (or was) parallel to them. This is necessary to avoid image distortions caused by the camera perspective. Align the Blue arrows against the Base item and Green arrows against the object you want to measure. The length of the object is shown in the top left corner of the screen. Method 2:Use screen as a traditional ruler. You can measure size of a small object by placing it on the device's screen and adjusting line limiters against the object. The size of the object will be show at the bottom of the screen automatically. If you see that ruler's scale is visually stretched/ shrunken, you can reset calibration manually. On-screen ruler can be calibrated using different Base Items, including Debit/credit card or coin. Double tap on screen to call settings. Accuracy:Given that you have accurately aligned markers, you will receive a measurement that is as precise as when using a traditional ruler or tape measure.