I am not old enough to remember the original Derby Lightweight units in revenue earning service, and only ever saw this one unit on the mainline when it was in use as the Ultrasonic Test Train. TDB975008 & TD975007 (formerly 79018 & 79612) head west at South Moreton on 12 September 1985 with an unidentified (apart from the fact that it is 6Z08!) working. I don't often bother with going away shots, but of course with DMUs there is little visual difference, in this case just the barely perceptible red tail lights and the fact that it is on the down relief line.