Abstract: A vehicle data recording system has connections to one or more analog sensors, and stores data from the sensor(s) in a memory during laps of a track. The system provides for analog/digital conversion for converting analog data from the sensor(s) into digital data, and triggers a procedure for storing of the data in memory. Periods of storing of the data in memory are automatically started and stopped. The system stores in memory a set of data for a datum period and has means for storing further sets of data in a memory. A set of data stored during a first period is compared with a set of data stored during a further period and one of the sets of data is selected for retention in memory in accordance with a predetermined algorithm. The retained set of data is compared with the datum set and differences between the datum set and the selected set are output.