Having a square, being it a try square, a carpenter’s square, a mechanics square, a speed ruler, combination square or whatever is necessary but often not enough. A big square is good for measuring big things like walls but more or less totally useless for dove tails and vice verse. There is also the problem with not begin able to use a square since the very corner is protruding or misshaped in a way.
So why not have square blocks to stack and clamp to each other. Make them non magnetic to not gather metal dust. Make holes in them to make it possible to clamp them together in various shapes. Make room for magnets to put in an take out to stack them. Make the surfaces so even that they stick like Johanssons måttbitar. Make other angles and radiuses.