Students of mine regard my mental math skills as nothing short of magic, which is concerning.
Was explaining a Wizz-wheel (circular slide rule) on the back of the DR Computer to some Air Cadets not too long ago.
They'd "found" the computer, but didn't have a scooby how to work it.
"OK" says I, "we'll work an example." They were doing an MS Flight Sim light aircraft trip IIRC.
"Airspeed?" (no wind for easy starters) "170 knots"
"Distance?" "51 nautical miles"
"Don't need the computer for that one - it's 18 minutes!"
I could not have made a greater impact if I had made sparks come from under my fingernails, and turned one of them into a frog!
O tempora o mores.