| 摘要 |
An all-purpose level in the form of a box that contains a ball rolling on an upwardly concave surface that is a figure of revolution about a vertical axis. The box rests on a member which will be horizontal when the level is in engagement with a truly vertical or horizontal surface. For this purpose, the member is disposed at a right angle to a plate which is hingedly connected to another plate about an axis perpendicular to the plane of the member. The member is selectively lockable in that perpendicular relationship; but when released, the member folds against the first-mentioned plate and the device thus folds about two hinges at right angles to each other, thereby to provide a configuration in which the level can rest on a generally horizontal surface to indicate true horizontal orientation thereof. Because the two plates are hinged to each other for swinging movement about the mentioned axis, the plates can be applied equally well against right angle vertical corners, or vertical cylindrical surfaces of any radius. The lowermost edges of the plates lie in a plane, when the plates form a dihedral with each other, which plane is parallel to the member that carries the box and so permits use of the device to indicate the horizontal orientation of an upwardly facing surface on which those lower edges are made to bear.
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