What is an Abney
A device used to determine elevation difference between an observer and a selected viewable location. It is sometimes called an Abney level or clinometer. It works by measuring the angle between an observer and a viewable point. The angle combined with the distance between the observer and the viewable point can give the elevation difference with simple geometry. An Abney is simple constructed, handheld, and easy to use and is therefore appropriate technology for the developing world and people without access to other common surveying and mapping tools. An Abney consists of viewing sight, a pendulum, and an angle scale shown in Figure 5.
Figure 5: A basic Abney Level