Precision squares are available in various qualities (squareness accuracy) based on the DIN 875 standard. These categories are in order GG2 (lowest) - GG1 - GG0 - GG00 (highest).

The precision square is a measuring tool used to determine whether an object or surface is perpendicular (at a 90-degree angle) to another surface. It consists of a long, straight blade fixed at a perfect 90-degree angle, forming an L shape. The blade is usually made of metal and has a finely finished edge that allows for precise measurement. Precision squares are commonly used in carpentry, metalworking, and other precision trades where accurate measurement is critical. They can be used to check the squareness of a workpiece or machine, adjust machines, or ensure that cuts are made at an exact angle. They are often manufactured with very tight tolerances..