Another cool one from my youth was the old-style bicycle speedometer, the one that had a little disc with a nib that caught on a spoke to make it spin. Even though it slowed you down some tiny, imperceptible amount, as a kid it was the coolest thing ever to see immediate feedback about how your wildly flailing legs translated into a few more MPH. Of course, it meant you spent more time staring at the dial than at the road ahead, and this is before kids all wore helmets. It’s surprising some of us survived childhood. (Oh, and I had to walk to school uphill both ways in the snow…barefoot.)