A vehicle accelerometer system comprises an accelerometer for installation in a vehicle, a processor for selection of accelerometer output data items for inclusion in an accelerometer output data set representative of measurements by the accelerometer at a plurality of different vehicle locations, each accelerometer output data item being representative of a respective measurement by the accelerometer, and a storage device for storing the accelerometer output data set, wherein the processor is configured to process the accelerometer output data set to determine an orientation output representative of the orientation of the accelerometer with respect to the vehicle.