The need for levelling instruments started when men wanted to erect monuments which were planed to last for ever.
The fact that a laser beam can be formed in such a way that it travels nearly parallel over a long distance, made lasers a valuable tool for defining a straight line. In all applications, like construction of buildings, roads, railway tracks or tunnel where straightness is an important parameter, lasers proved their superiority. The construction of the railway tunnel across the English Channel started from France and England simultaneously, the two groups met with an offset of a few centimetres, a brilliant performance of the engineers and the used laser for levelling.
The straightness and low divergence of the laser beam are the properties which are exploited for this technique. By means of a simple laser beam, huge road construction machines are guided along a perfectly straight line and during the construction of buildings, the straightness of floors can be adjusted. By means of imaging optics the laser beam can be transformed into a line and even into a rectangular cross which, for instance, is used for positioning objects with respect to a handling facility or a machine. Light lines and even crossed lines are important in sawmills to align the saw blades with respect to the logs. Furthermore, stonemasons use light lines when cutting valuable boulders.

Principle of Operation

In the example, a laser spirit level is attached to the tripod. The system is positioned in the room in such a way that the laser spot hits the reference point of the to be transferred height. The spirit level is adjusted horizontally also for the 90° rotated direction. One may now check if the craftsmen who built the object of interest did a good job.
In the next example, laser levelling as well as range finding will be applied. The room needs to be divided exactly into two halves. For this purpose the 90° beam bender must be used.