The accelerometers at the heart of the StopOMeter app need to be calibrated before use otherwise you might get spurious results.
The raw iPhone accelerometer values can show an error of up to 10% which can be corrected for by selecting Information > Calibration.
The calibration screen consists of three bars, with superimposed accelerometer values. Each bar has a contrasting centre stripe which indicates the amount of variation for the current calibration settings.
If the iPhone has not been calibrated, then Not Calibrated will be displayed at the bottom of the screen.
To begin calibration, find a flat surface to work on and press the [Calibrate] button and select Calibrate from the pop-up menu. A large arrow will appear on the screen. Orientate the iPhone on the edge indicated by the arrow and move it so it is vertical. Once the local vertical has been sensed for that edge, you will hear a beep and the next large arrow will be displayed pointing to the next edge to be sensed. The order of sensing is left edge, right edge, bottom edge, top edge, screen up and finally screen down. The display will change to give you the date and time of the calibration. You will notice that the contrasting bars are no longer aligned with the main bar, which indicates the degree of error found in the accelerometers.