Ever need a square and you don’t have one? If you don’t need extreme precision, this will at least allow you to strike a line straighter than freehand.
I was doing a project and being intentionally minimalist. I wanted to strike lines across a 1×2 to guide my eye for hand sawing. I grabbed one of my glue cards, folded in in half and presto, I had something like a square.
-- Ni faru ion el ligno!