 Topographic Abney level

The Abney level is an instrument used in surveying and topography to measure the angle of slope or the elevation of terrain. It consists of a graduated scale, typically a circular or semi-circular arc, and a sighting device, allowing surveyors to determine vertical angles and distances. The Abney level works by allowing the user to sight a distant object at the same height as their eyes while simultaneously measuring the angle of elevation or depression.