Slide rules, used to love them. As a Marine Engineering student at Sydney Uni (Australia) in the early seventies, calculators were very basic and we weren't allowed to use them anyway. So it was Long hand, Log tables or a slide rule. The slide rule was by far the quickest, you just had to be careful when keeping track of the decimal point. They were in their own when it came to doing calculations involving raising a value to a power that was not a whole number as in 2, 3, 4 etc. calculations on the expansion and compression of gases in particular often involve a power of 1.3 or 1.4 etc.
I still have a couple of good old Japanese bamboo slide rules, they were the best. And a circular one as shown above, they were particularly good at trig calculations,