Hmmm -- during flight test of the very first B747 FMS, aboard RA1, the test-engineers had the cockpit video operating.
After that B747 suddenly turned away from the planned arrival course, all the test crew were mystified.
Later into the night, after that failed test, the test engineer re-watched the video :
Dale's right forefoot was resting on that foot-rest,
the edge of his shoe-sole tapped the INSERT button on the #1 Delco INS --> sudden sharp turn .
This is a good example of why cockpit video cameras should be mandatory. Voice recorders and data recorders can pick up a lot of things but a video recorder would have this incident resolved very quickly.