In surveying and construction, the laser level is a control tool consisting of a laser beam projector that can be affixed to a tripod, which is leveled according to the accuracy of the device and which projects a fixed red or green beam along the horizontal and/or vertical axis.
Laser level Wikipedia
The concept of a laser level has been around since at least the early 1970s, the original spinning-mirror design laser plane and line level was patented by the late 1980s, and the compact lens-based laser line level (as produced by many tool manufacturers today) was patented in the late 1990s.
A rotary laser level is a more advanced laser level in that it spins the beam of light fast enough to give the effect of a complete 360 degree horizontal or vertical plane, thus illuminating not just a fixed line, but a horizontal plane. The laser beam projector employs a rotating head with a mirror for sweeping the laser beam about a vertical axis. If the mirror is not self-leveling, it is provided with visually readable level vials and manually adjustable screws for orienting the projector. A staff carried by the operator is equipped with a movable sensor, which can detect the laser beam and gives a signal when the sensor is in line with the beam (usually an audible beep). The position of the sensor on the graduated staff, also known as a grade rod, or story pole, allows comparison of elevations between different points on the terrain. Most laser levels are used in the construction industry.
A tower-mounted laser level is used in combination with a sensor on a wheel tractor-scraper in the process of land laser leveling to bring land (for example, an agricultural field) to near-flatness with a slight grade for drainage.