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 sq. equivalent to 5 inches, Back: 1 cm length 50 cm Length tolerance: ±0.2 mm cm,等效于仪表尺度±0.4 mm 平方角:100 mm不超过±0.1 mm