This is a good brand name square my father bought. When I used it I discovered it was not actually square. The rivet and brass system for attaching the blade to the handle is very good. No amount of tapping would change the alignment.
Step 1: Checking a square
If you want to check a square, you could hold it up to another square, but that one could be inaccurate, too.
The dark brown piece of wood in the photo is the end section of a piece of veneer plywood I have been carrying around for several decades. The white paper arrow points to the factory cut edge of the sheet. This makes a trustworthy straightedge. The white chipboard piece of shelving raises my work surface for this Instructable to the same height as the plywood straightedge.