It's a trackball. Back in the Elder Times, before tiny lasers and sensors were a thing, a computer mouse worked by having a little ball inside, with rollers to tell where the whole thing went. A trackball was basically that, but flipped upside down, so you have a stationary box with a billiard-sized ball that you roll around with your hand to move the pointer around. They're still made, but it's very much a specialty product anymore.
last edited at Jan 31, 2020 11:28PM