The flight stands use different heights of panel pins – 50mm, 40mm, 30mm and 20mm – for the four different height levels (although I originally used 13mm for the lowest level and 40mm for the highest).
I just swap them over when an aircraft dives or climbs. These were my prototype ones:
Sorry to interrupt Keith, but I forgot to say “thank you” to Jim for taking the time to snap a few photos of his different sized flight stands. They look quite good, and give a much better visual representation of altitude than a mere die.