Slide rules are annoyingly imprecise. I had to learn how to use one in high school chemistry in 1975 or thereabouts, and it was a bit faster than doing the math on paper, but still annoying. And I had a pretty good slide rule, because I found the one my much older brother had used when he was in high school. By the next year, they decided that everyone could probably afford calculators, and we started using those.