External base point and inner scale With name space Length side (mm): 520 Short side (mm): 265 Width (mm): 15 Thickness (mm): 1.1 Scale specifications: Front: 1 shaku equivalent 1 shaku equivalent 5 sun, Back: 1 shaku equivalent 1 shaku equivalent 5 sun Length公差:cm±0.2 mm,shaku等效±0.4 mm 平方角:100 mm不超过±0.1 mm