You can use a drywall square by performing the following steps:
Set up the square on the plaster board by aligning the stock with the edge of the drywall. The blade will run down the surface.
Measure where you want to cut, and mark it using the hash marks along the blade.
Hold the square securely in place, and use the blade as a straight edge so you can cut the material along your mark.
If you’re looking for a drywall square that you can use on your next project, be sure to look at what we have at Engineer Supply.