A system using an accelerometer to determine a frame of reference, for subsequent use in assessing or monitoring a status of a vehicle, or operator thereof, comprising: a data collection and assessment system mounted to the interior of a vehicle, the data collection and assessment system comprising one or more data collection devices, including one or more accelerometers, that collects information from the one or more accelerometers as the vehicle is moving; and a frame determination module which samples or otherwise receives accelerometer data, collected as the vehicle is moving, over a period of time including changes in acceleration and deceleration provided by instances of braking, and also information from one or more other on-board devices, and uses this information to determine a frame of reference for the system relative to the moving vehicle, wherein the frame determination module determines the frame of reference by sampling the accelerometer data, and: determining averages of the accelerometer data over a period of time to determine the moving vehicle's x-y plane; averaging the accelerometer data over several braking instances to determine the moving vehicle's y-axis; using the determined x-y plane and y-axis of the moving vehicle to determine the x-axis and z-axis for the moving vehicle; and thereby determining a rotation matrix that reflects the skew between the system's orientation and understanding of direction, and the vehicle's true orientation or direction in three-dimensions, thereby allowing corrections to be made to the system accelerometer data to more accurately determine the vehicle's true orientation/direction and motion. a data collection and assessment system mounted to the interior of a vehicle, the data collection and assessment system comprising one or more data collection devices, including one or more accelerometers, that collects information from the one or more accelerometers as the vehicle is moving; and a frame determination module which samples or otherwise receives accelerometer data, collected as the vehicle is moving, over a period of time including changes in acceleration and deceleration provided by instances of braking, and also information from one or more other on-board devices, and uses this information to determine a frame of reference for the system relative to the moving vehicle, wherein the frame determination module determines the frame of reference by sampling the accelerometer data, and: determining averages of the accelerometer data over a period of time to determine the moving vehicle's x-y plane; averaging the accelerometer data over several braking instances to determine the moving vehicle's y-axis; using the determined x-y plane and y-axis of the moving vehicle to determine the x-axis and z-axis for the moving vehicle; and determining averages of the accelerometer data over a period of time to determine the moving vehicle's x-y plane; averaging the accelerometer data over several braking instances to determine the moving vehicle's y-axis; using the determined x-y plane and y-axis of the moving vehicle to determine the x-axis and z-axis for the moving vehicle; and thereby determining a rotation matrix that reflects the skew between the system's orientation and understanding of direction, and the vehicle's true orientation or direction in three-dimensions, thereby allowing corrections to be made to the system accelerometer data to more accurately determine the vehicle's true orientation/direction and motion.