# How did scientists and engineers actually use slide rules, in the old days?

**URL:** <https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784>\
**Category:** Factual Questions\
**Created:** [September 3, 2015, 4:37am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784 "2015-09-03T04:37:48Z")\
**Posts on this page:** 1\
**Page:** 6

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**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\
**Post date:** [September 12, 2015, 5:13am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/101 "2015-09-12T05:13:09Z")

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It looks like they used the table to iterate the entire division, two bits at a time instead of one. This cut the time for division in half, compared to the much simpler but slower method of iterating one bit at a time. For a 64-bit number, which has a 53-bit mantissa, this would mean 27 clock cycles instead of 53. One would think that time could be saved if the remainder zeroed out, finishing the operation early, but I suspect that the logic to implement that might not be worth the potential savings (division is a comparatively low-traffic operation in computers).

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