The dumpy level is one of the most basic types of optical level instruments. It is used in surveying and building to find elevations, which are known as levels. It can be used to set, measure, or transfer horizontal levels. Some surveyors have replaced this older style of instrument with automatic levels, laser levels, or other high-tech optical level instruments. One common variation of the dumpy level is the tilting level, which allows for less operator error.
Surveying is used to find the height of buildings and earth topography. This information can be used to make maps, set boundaries, and gather information for builders. Measurement generally starts from a benchmark point, the height of which is known from a previous survey. The surveyor may also use an arbitrary point and estimate its height.
The main body of a dumpy level is a telescope that swivels to take 360 degrees of measurements. Magnification power can range from 20 to 30 times. Many have spirit levels, the same kind found in simple construction straight edges, built into the base so the operator can clearly see if the device is level. When the bubble stays in the exact center no matter how the telescope is rotated, the device is level.
Three leveling screws set over a foot plate allow the dumpy level to be minutely adjusted. Each quadrant of the level must be set in order to ensure an accurate reading no matter which direction the telescope is pointed. These levels are mounted on tripods to hold them at eye level and keep them stable during measurement.
Finding elevations using a dumpy level takes at least two people, an operator and an assistant. The assistant holds a tape measure or marked staff, called a leveling rod, vertical to the point being measured. Meanwhile, the surveyor looks through the eyepiece at the target and the leveling rod. The operator takes measurements by comparing the marks on the leveling rod to the landscape. Several measurements of the same area can be used to find elevation, distance, and other qualities of the landscape.
A tilting level is a type of dumpy level that allows for greater accuracy. Instead of being welded to the level, the telescope is hinged. This allows the eyepiece to be flipped 180 degrees without adjusting the head. As the level needs to be moved less, errors are less likely to occur.