Minty, I used to have one of those circular slide rules. GREAT invention! I can't recall what happened with it, but man, I used the heck out of that thing until someone showed me a device that just blew me away. I eventually bought this HP hand-held calculator, model 45, that did everything in Reverse Polish style. But it had a 50-step program memory and did 10-digit precision on its math and it had 10 registers accessible from the programs. It was all I needed to do linear regressions for the formulas for my dissertation. In fact, when the school's big beastie had a massive circuit failure due to lightning hitting the school's power distribution box (and back then, power conditioners were not common appliances), it was better than their leftover early-3rd-generation computer, which was all they had left until the big beast got fixed.