This is a picture of a Z-Square. It is very useful for building 3 dimensional frames. You can make them any size you like.

To assemble them, just clamp each of the 3 sides to a layout table, and square them as you go. As long as all 3 sides are square, the whole thing is square.

This is a picture of a tiny one I made for TIG welding tube frames. I have made them up to 8 feet tall.

The big ones are a pain to store unless you have a hook in a corner of your ceiling.

Someday I will tackle making a folding one.