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 6 sun, Back: 1 shaku equivalent 1 shaku equivalent 6 sun Length公差:cm±0.2mm,shaku等效±0.4mm 正方形:100mm不超过±0.1mm