Squares

Next to my handy Irwin Quick Grip clamps, my favorite tool is my speed square. It's an indispensable item, especially if you're doing a lot of work with a circular saw. Cross cutting is a breeze using a speed square, resulting in lovely straight cuts, and it's also nice if you're doing a lot of 45 degree miters. Plus it's light, and when you really screw up and spike it on the floor of your workshop, the blow doesn't throw it all out of whack.

But I've gotta plead ignorance here: What's with all the additional markings on a speed square? I know it can be used for all sorts of things like rafters and stairs, but I have no clue how to read it. Math was never really my forte, and this involves numbers. It makes me, like, all confused. Anyone have any tips?

I also have a framing square, and honestly it sits in my tool bag and doesn't often see the light of day. Then I happened to read this article on This Old House and realized that you can use it to scribe nice straight lines when you need to rip a board. Nice.