You could also have a lot of fun with setting the Variation to whatever value was required. We often flew a" single heading " from Hong Kong to Singapore, despite a track change of 20 degrees as we passed Vietnam, by judicious use of the Variation Setting Control. Some pilots queried why some Navs called for a heading change but others did not. We never told them!
Flying Grid/Gyro also had its amusing times as the pilots tried to resolve the Grid heading with the Magnetic Heading. One month at Marham we flew on Grid for "Navigator Training" with a Grivation of 180 degrees,ie North is South. You departed Marham and flew "South West" to the North Sea. Watching the pilots turning in their seats to try to read the conflicting headings was great fun. After a month we were told to stop it.