A combination square is one of those must have tools for a woodshop. Choose etched lines and numbers over painted ones. They will last longer.
$8 and up.
Buy
I have a six inch, a twelve inch and a 16 inch combination square. I use them for every project. Starrett are of course the best, but the Emprie brand is more affordable without sacrificing quality and Empire has a lifetime warranty and is made in America.