Crossed square box by JB / T3411.56-99 standards for manufacturing, material is HT200. Mainly used for parallelism, verticality and other parts of the inspection and marking. Square box is a concrete cube cavities 6 Face made of cast iron or steel, which has a work surface V-groove. Square box test of the environmental conditions: room temperature, and humidity. Crossed square box requirements: Face crossed each square box can not have rust, other defects scratches, cracks, dents and the impact of the performance measurement. Non-face to be painted sand, edge chamfering. Crossed square box accuracy: for scraping flat square box in addition to test-givers, but also in contact with the coloring method test spots. In the side length of 25mm to any square within a few spots are: 1, 2 less than 25 points; 3 less than 20 points.