Illustrated Self-Guided Course on How to Use the Slide Rule (2012)
sliderulemuseum.com
sliderulemuseum.com
More specifically, I allow the user to slide logarithmically marked rules for two of the variables (and the calculator finds the third). Besides mapping well to Ohm's law and the way resistors are used in hobbyist electronics, I thought it was a fun way to explore various values for resistors, voltages, etc. More interactive than the "enter in two values get a third" text-field approach (although you can do that too if you want more precision).
https://en.wikipedia.org/wiki/Have_Space_Suit%E2%80%94Will_T...
Here's my post on Google+ about it [1]
I find it interesting that the pocket calculator quickly killed the slide rule, but did not kill the abacus.
Simple, effective, reliable.
This was cool as well though. Learned something more valuable today.