I wrote this a number of years ago, then forgot about it. It will be familiar to the geezers, but you young folks may want to try it out before tossing it in the garbage can. The relevant file is scale.pdf and it will let you do many of the things you could do with a slide rule. If you have some dividers, it will let you do anything you could do with a slide rule. Now, if you think that's a relic of the past, you're right. But you should also know that it's valuable when you want to get two or three significant answers to a problem, especially when no calculator is handy. The other file is some documentation.