When I was in high school, the first four function calculators came out. They were, like $200. Couple of the rich kids had them.

In chemistry class, we were doing "converting to standard temperature and pressure." The equation ended up being three numbers on the top of the divisor line, and two below. Teach gave 4 points for getting there, and one extra for actually doing the calculation. Three significant figures was all we needed. I used my slide rule, and did it in a fraction of the time it took the calculator guys. Pissed em off mightily. Most of the other kids didn't do the longhand thing, cause it took waaaay long to do.

You know that the Empire State building was built with calculations using a slide rule. I would bet the Brooklyn Bridge, too. And I think the early space program was run on slide rules, too. You see, beyond three significant figures, it is not really feasible to even measure some of those distances/weights/speeds. Back then, of course. But even now, you can calculate far more digits than you can really use.

Saul