This standard specifies cylindrical squares, rectangular squares, rectangular knife-edge squares, triangular squares, knife-edge squares, wide-seat knife-edge squares, plane squares, plane squares with seats and wide-seat squares ( Collectively referred to as "square or 90° square") terms and definitions, types and basic parameters, accuracy grades, requirements, inspection methods, signs and packaging, etc. This standard applies to squares whose measuring surface length L is less than or equal to 1600mm.