The performance of driver testers is monitored by supervisory driver testers whose activities in turn are controlled by a chief tester. Supervisory testers also, from time to time, travel in vehicles while tests are being conducted in order to observe at first hand the performance of the tester, to permit subsequent discussion of the test with the driver tester, and to make suggestions for any changes in conduct. In addition, test results are analysed by reference to test centres, individual driver testers, categories of vehicles, and region, in order to identify significant variations in results and to take any necessary measures to ensure uniformity of standards. Training and re-training of testers is also carried out.