If the relative position of two points is described by the 3D orientation of a line joining them, then, in general, tilt is the angular amount that the orientation has changed, in a vertical plane, from a previous direction or from a reference direction. If the original or reference orientation is nearly horizontal, then the term “tilt” is usually used. If it is nearly vertical, then the change is o£en regarded as “inclination.” Here, “tilt” will refer to either. œe two points can be separated by a discernable amount, the base, or the tilt can be measured at a point with the reference orientation being deŸned by the direction of the force of gravity at that point.œus, the same instrument that measures tilt at a point can be called either a tiltmeter or an inclinometer (or clinometer), depending on the interpretation of the results. œe instrument used to measure a series of tilts along any vertical orientation is o£en called an inclinometer (e.g., ).