OK many will not even get the play on the word especially if you are under 40 and I am not referring to the playground slide (slippery dip for the Aussies) rule of feet first fiercely enforced by many playground enforcement teams at elementary grade schools. In engineering many years ago before a calculator was under 20 pounds most engineers relied on their trusty slide rule as much as their pocket protectors. OK so I was joking about the pocket protectors, but every engineer was proud of their slide rule and could operate it pretty darn fast.
I just ran across a wikipedia article showing a slide rule (slipstick) and how to use them.
The scales on the front and back of a K&E 4081-3 slide rule.
When I was a sophmore in high school they taught us how to use a slide rule. The next year they didn’t say anything about slide rules and everyone had calculators.
Here’s an online sliderule
http://www.syssrc.com/html/museum/html/sims/javaslide/