This app is intended for entertainment purposes only and does not provide true speed measuring functionality. The readings are subjective to how well you calibrate and use the app.
Point your camera to the street perpendicularly, press calibrate, and start measure speeds by tracking the cars with your camera. Simple as that!
Enter your height, hold your phone to shoulder level (that is you normally do), point the thin red cross perpendicularly to the lane where cars are crossing and press CALIBRATE. Now you just have to follow the cars to get their speeds!
metric and imperial units.