I build a lot of things. Over the years, the Starrett combination square has become the essential tool. Nothing else comes close when it comes to measurement, laying out joinery, and checking machines. It really only does one thing - Precise measurement at 90 or 45 degree angles - but it does that so well, it becomes super versatile. I've used it on every single project in the past five years, and my work is better for it. Mine is relatively new, a gift from Colleen's parents, but there are tons of decades-old Starretts still in use.