What is a clinometer?

A clinometer is an instrument used by civil engineers and surveyors for measuring angles of inclination of slope and hills. It is also used to measure the height of an object if the distance from the observer to the object is known. It is also called Abney level. Clinometers measure both inclines (positive slopes, as seen by an observer looking upwards) and declines (negative slopes, as seen by an observer looking downward) using three different units of measure: degrees, percent, and topo. Astrolabes are inclinometers that were used for navigation and locating astronomical objects.

In aircraft, the "ball" in  or turn and bank indicators is sometimes referred to as an inclinometer.

Early inclinometers include examples such as Well's inclinometer, the essential parts of which are a flat side, or base, on which it stands, and a hollow disk just half filled with some heavy liquid. The glass face of the disk is surrounded by a graduated scale that marks the angle at which the surface of the liquid stands, with reference to the flat base. The zero line is parallel to the base, and when the liquid stands on that line, the flat side is horizontal; the 90 degree is perpendicular to the base, and when the liquid stands on that line, the flat side is perpendicular or plumb. Intervening angles are marked, and, with the aid of simple conversion tables, the instrument indicates the rate of fall per set distance of horizontal measurement, and set distance of the sloping line.

One of the more famous inclinometer installations was on the panel of the Ryan NYP "The Spirit of St. Louis" - in 1927 Charles Lindbergh chose the lightweight Rieker Inc P-1057 Degree Inclinometer to give him climb and descent angle information.

The clinometer is mainly used to measure the angle of slope. If set on a slope it can be used to give the angle of inclination of the surface. With the arc set at 0 degree, it can be used at a hand level.