My reference is an iGaging machinist square. 4 inch for about $15. Square is square. My cheap carpenters triangles are square. My drafting triangle is square. My Japanese combo square is square. ( and 45) Combination squares, if high quality and iron/steel heads can be square, but they wear over time. None of my zinc head combo squares was still square. Rather than screw with them, tossed them and bought new better quality Chinese ones. Mostly iG, but not all. Nothing against Starrett or other premium machinist tools, but not at all necessary. You can buy one Starrett, or a whole suite of other quality tools for the same price. Your money.
I kind of like the Japanese square as it is thinner. Mine has mm markings even though Amazon showed inches, but it is too handy to send back. About $20. Woodcraft has the inch ones on the shelf for $30.
I recently bought bundles of rulers with all combinations of markings off Amazon. All well made, SS, etched, accurate. Again, nothing against Woodpeckers, Incra, Starrett, but if a $5 ruler is the same quality as the $90 ruler, well you decide.