A method for recording and predicting position data for a self-propelled wheeled vehicle (1) carrying a load (14) is provided whereby the vehicle (1) is caused to move along a ground surface (5) along a predominantly straight line trajectory (17) by rotating at least one load carrying wheel (3) in frictional engagement with the surface (5), angular rotation data of at least one wheel (3) is obtained, absolute position data are obtained at different predetermined fixed positions Pn of the vehicle (1) with respect to the surface (5) along the straight line trajectory (17), whereby the distance travels is measured independently and used to calibrate motion sensors on board the vehicle. The invention also comprises a delivery or pick up system, a program for an on-board computing device and an on-board computing device.
