A watch with a Tachymeter can be very useful. Many moons ago, when flying Shacks from Ice Station Kilo, when we came 'off task' over northern waters, I would use the Tachymeter to measure groundspeed, using the Saxa Vord Tacan. I would then calculate ETA ISK and tell it to the crew. It was always very accurate, much to the consternation of our two, very senior, Navigators.
One night in the bar, post-flight, they asked me how I did it. When I showed them my watch and explained, they both roared with laughter and bought me a pint - each.