I gotta post something, so I'll post the mechanical calculator that the flight school wanted me to get. How it works is that you can set ratios in the dial and multiply them. In this picture, it's 60:10 (or 60:1.0) so I can take any number from the inner circle in minutes and find out how many hours that is equal to on the outer circle.
There are also other things on this calculator, including a wind vector calculator, and charts. Most pilots don't use these anymore, but they still wanted me to know how to use one
I've got a very rudimentary version of that on my watch! I didn't specifically want an aviation watch, just something radio controlled, solar powered, and resilient. This one is made with titanium and has sapphire instead of glass.
ETA: I've read the manual and a few articles on how to use the damn thing and I still don't get it. I usually forget that part of the display rotates with a dial.