Speaking of things meant to be square, I offer the humble plastic speed square. They are fine as-is for general construction carpentry, but they lack the 90 degree reference bench work demands.
My Starrett 12" combo square acts more as a reference tool on my bench than a layout tool. I also have a couple Starrett 6" combo squares which work perfectly for the smaller work I tend to do. But then I have three plastic speed squares, and I've used a hand plane to bring the height edge of the speed square into square with the base of the speed square. A few minutes of time to level any high spots, or to turn 89 or 91 degrees into 90 degrees, then I can keep the big Starrett in its place, and let these plastic speed squares taking the knocking on the bench.
I reference the Starrett beam/rule to the inside of the base section (as the photo shows), not the outside of the base section. And only the height edge of the speed square gets tweaked with the plane, the part that has the base of my Starrett engaged against. Those are 7", 8", and 12" speed squares. I prefer the plastic to aluminum speed squares because of the ability to easily tune them into square.
A note on combination squares- I'd suggest against the cheap hardware store combo squares made from cast aluminum or other mystery metal. The rules tend to wear that soft metal base pretty easily while sliding the rule, making them go out of square. (I also push against the spring loaded tightening bolt when sliding the rule to remove that spring pull action from pulling the rule against the base to help prevent wear.) There is always a temptation to buy old Starrett, or other quality brand antique combo squares, but those are typically pretty worn in the slide section, preventing getting 90 degrees. I'd suggest new.