it carefully each time he sights on a rod on another point. It also reduces the effect of minor settling of the tripod to the actual amount of motion instead of leveraging the tilt over the sight distance. Three level screws are used to level the instrument. Laser level Laser levels project a beam which is visible and/or detectable by a sensor on the leveling rod. This style is widely used in construction work but not for more precise control work. An advantage is that one person can perform the levelling independently, whereas other types require one person at the instrument and one holding the rod. The sensor can be mounted on earth-moving machinery to allow automated grading. See also Astrogeodetic levelling Glossary of levelling terms Survey camp Land levelling Orthometric height Dynamic height Physical geodesy References External links USALandSurveyor Differential leveling video tutorials E-Learning-site with online-exercise for differential levelling Differential levelling online calculation Civil engineering Geomatics engineering Surveying Vertical position