| 摘要 |
To establish as a plumb reference line for construction of buildings or shafts a laser beam is used. A laser source is mounted in a tube, the upper end of the tube is supported so that the weight of the tube and laser source makes the tube assume a vertical position. The support may be mounted on a tripod or side support. For shafts, the laser beam is directed downward. For buildings, the source may be reversed in the tube to be directed upward.
|
