A machinist square is the metalworker's equivalent of a woodworker's try square. The square refers to the tools primary use of measuring the accuracy of a right angle (90 degrees). To "try" a surface is to check its straightness or correspondence to an adjoined surface. A small notch has been added to the inside corner of the square to prevent small particles from accumulating and affecting the square's reading.
This Bulgarian made small machinist square has a 40mm (1-5/8") long foot and stands 50mm (2"). It also has a graduated scale along both sides of it's height (50mm on the outside and 25mm on the inside. Unlike the less expensive India made machinist squares that are welded together from 2 pieces of material, this square is machined from one piece bar stock (billet). Made from stainless steel (INOX) and has a back accuracy in accordance with DIN 875/II (DIN875/2) standards.