An inclinometer or clinometer is an instrument for measuring angles of slope (or tilt), elevation or inclination of an object with respect to gravity. It is also known as a tilt meter, tilt indicator, slope alert, slope gauge, gradient meter, gradiometer, level gauge, level meter, declinometer, and pitch & roll indicator. Clinometers measure both inclines (positive slopes, as seen by an observer looking upwards) and declines (negative slopes, as seen by an observer looking downward).
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 line 0.——0. being parallel to the base, when the liquid stands on that line, the flat side is horizontal; the line 90.——90. being perpendicular to the base, when the liquid stands on that line, the flat side is perpendicular or plumb. Intervening angles are marked, and, by 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.
The earliest electronic inclinometers used a weight, an extension, and a potentiometer. Early in the 1900's (circa 1917) precision curved glass tubes filled with a damping liquid and steel ball were introduced to provide accurate visual angle indication. Common sensor technologies for electronic tilt sensors and inclinometers are accelerometer, liquid capacitive, electrolytic, gas bubble in liquid, and pendulum. MEMS (Micro-Electro-Mechanical Systems) technology is becoming the new standard due to their tiny size and low cost.