I taught a private class this past weekend, and the student mentioned that a post about all of my squares would be cool. After giving it some thought, I realized that each of the squares I own has a specific use (or uses), and none of them are extraneous. Generally speaking, all of my squares are layout tools, and I prefer my layout tools to be small. They are easier to hold in place because of their size and weight. However, a few of them are used for setting up tools, like my tablesaw and jointer, and I do use them to check that my milling and cutting produces square results.
Squares must be accurate, so it’s important to buy ones that are high quality. That’s why all but three of mine were purchased new from companies that are easy to deal with if a tool isn’t accurate. As for the three used squares, I was able to check their accuracy before I acquired them. So, if you like flea markets, antique malls, and estate sales, learn how to check that a square is actually square. And you can learn how at the end of this post.