A small pocket-sized protractor, perfect for checking right angles. It's easy to print and inexpensive, so even if you lose this little red square, you won't be too upset about it.

I've already checked it with a high-end protractor, and it's very accurate! I'll print a dozen of them and place them in the workshop.

Even with a fine setting of 0.12 mm, this can be printed within 30 minutes.