Abstract The analysis of tachograph charts is an established part of accident investigation by police in the U.K. The seizure of the chart, collection of data from the accident scene, and examination of the tachograph installation in the vehicle are all carried out by trained police officers. The analysis of the chart to determine speeds and acceleration rates is a specialised skill performed in the forensic science laboratories. Police training in tachograph examination for accident investigation is confined to a small group of officers in each force, and is particularly concerned with the calibration of the instrument. Techniques are taught for checking the calibration whatever the state of the vehicle. The laboratory analysis consists of reading with a special microscope the speeds shown by the chart during the seconds immediately before an accident and adjusting the figures according to the results of the officer's calibration checks. Care is also taken to check for any defects in the instrument or for artefacts, by analysing the record for several minutes before the accident, so that at least two significant features on the speed trace may be matched with actual features on the route taken by the vehicle.