An Abney level is a surveying device used primarily in preliminary surveys to collect basic information about height and grade. The device consists of a hand level intended to be held at eye level, with an attached protractor the surveyor can adjust to collect information about a landscape. Surveying supply companies carry a range of Abney levels, including devices offering magnification through the eyepiece for more distant sightings. People are taught to use this surveying tool early on in their careers, as hand tools can be very useful for many surveying tasks.
This tool is named for Sir William Abney, a British man who lived in the 19th century. It includes a tube with a bubble level inside and an eyepiece at one end. When people look through the eyepiece, they can see the surrounding landscape, along with the bubble. After centering the bubble on a target of interest, the protractor can be moved to find out the angle. Using trigonometry, it's possible to determine the height of objects in the landscape, and the surveyor can also find the grade.
Usually, a surveying team uses an Abney level. One person holds the device and the other person serves as a height reference. People can also work with poles marked in increments if another person is not available. As people take sightings, they note their findings and use this information to develop a preliminary report. Measurements taken with an Abney level can be very accurate when the user is experienced and it is properly calibrated, but they are usually confirmed with a more extensive survey later.
Like other tools used for measuring, the Abney level needs to be well cared for. The device should always be calibrated before use, using known objects to confirm that the protractor is properly adjusted. If it is not, it can be moved until it aligns properly. If a storage case is provided, it should be used to store the Abney level when people are not using the device, to reduce the risks of damage.
Surveying is performed for a variety of reasons, from developing and updating maps to preparing ground for construction. Surveyors can work for private companies, as well as government agencies, and in their work, they use an assortment of tools. Learning to work with basic hand tools can be an important part of training, as it allows people to quickly and inexpensively get a thumbnail overview of an area of interest.