Its history is fascinating. Sometimes referred to as a rafter square, the Speed Square facilitates any number of layout operations from marking out and cutting walls to laying out rafters.

The Rafter Square, or Speed Square, does more than mark perpendicular lines. Here's how to make sense of all the numbers on your square and get the most out of this tool.

A speed square is handy for marking cuts, finding angles, and more. Here are a few good reasons why no toolbox should be without one.