Speaking of obsolete technology: Circular slide rule
I really liked circular slide rules—I had one that was 8″ in diameter, which produced a VERY long scale compared to the regular slide rules. I just listed one on eBay, but it’s a pocket model and just chockablock with useful constants and tables (on the back and on a two-sided pull-out). Quite cute, but I think their day may have passed. As with the pocket chess set, modern technology offers other solutions. But I do like the little guy.