..... calling it a "Circular slide rule ".
Ditto, even have a 2" ( sorry 50 mm ) , once a keyring version, stuck inside my wallet to help me - in the days before unit pricing - decide that the Supermarket was scamming me by offering larger sized packets at a "special" price instead of buying 2 at the "regular" price, or whatever, as they always do. One day the teenager on job experience at the check out asked me what it was, and on being told said " What's a Slide Rule "? and I've similarly been asked " What's a Sextant " One could weep