Hello people, Given acceleration data in Gs (9.8m/s^2) in world's coordinate, we should be able to determine distance traveled by subjects. However, a considerable amount of samples tell me that the subjects were moving at 12~20 m/s at then end of the walking phase. That is faster than Usain Bolt.... :( This seems to attribute to the fact that some samples have systematically biased acceleration values in the direction of movement. I know that the iphone accelerometer and gyroscope are suppose to be noisy, but I am surprised by 100-200 m offset that I sometimes get. Does the testing app calibrate accelerometers before testing? Also, is anybody else observing the same trend? Nao