| 摘要 |
Fixed on the board (1) is a support (8) in which is rotatably mounted a shaft (7) which is rigid with two pulleys (5a, 5b) each cooperating with guide means (3a, 3b) respectively for the straight-edge. Mounted between the support (8) and the shaft (7) are a rotary sleeve (14) and a spring which is wound around the shaft (7) and is rigid (at 19) with the shaft and (at 17) with the sleeve (14) in the support (12) but is withdrawable so as to permit the regulation of the torsion of the spring (18) and the balancing of the straight-edge. |
