Calculus is actually useful and not as hard as people think if you get the right explanations. This isn’t exactly a slide rule, but since it is a mechanical math device, we think it counts anyway.

But there was a time that it was common to see an engineer with a stick hanging from his belt, instead of a calculator or a cell phone. A Pickett brand slide rule flew to the moon with the ...

The slide rule was the evelution of Napier's Rods (or bones) which where used for multiplication. Before the electronic calculator, in 1974, the slide rule was used by scientists and students to ...