| 摘要 |
<p>The protractor is used in mechanical construction and building operations to check or establish slopes. Problems of using bubble levels are overcome by use of a fluid-damped pendulum to provide a vertical axis. The protractor (1) comprises a rectangular body with two plane and parallel sides (2,3). A pendulum (6) is mounted to rotate freely around a transverse axis (7) within a transparent sealed enclosure (8). A window (12) with lateral boundaries (10) carries a scale (14) graduated in angular degrees, against which a pointer (15) on the pendulum rotates. A float (19) makes the density less than that of the damping fluid within the enclosure, and also places the centre of gravity away from the axis.</p> |
