| 摘要 |
A rectangular block is provided made of a transparent plastic (1) containing a glass ampoule (2). The ampoule is centrally placed within the block, and is precisely parallel to the longitudinal axis of the block. The ampoule contains a coloured liquid, and an air bubble (3). - The ampoule is marked with two indelible marks to indicate the central position for the bubble. A hole (4) is bored along one edge of the block, parallel to the longitudinal axis. A string is threaded through the hole so that the device indicates whether the string is horizontal.
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