In its most general sense, the term “inclinometer” refers to any device for measuring with precision the angle between a surface and a line that is perpendicular to a line through the earth's center of gravity – or, in other words, level. The difference between a level and an inclinometer is that while a level tells the user whether or not a surface is level (or plumb), an inclinometer tells the user exactly how far out of level (or plumb) it is.
In addition to ones used by carpenters or machinists, various forms of inclinometers are widely used in other fields – by plumbers, surveyors, miners, skiers, artillery gunners, sailors (to tell how far over a vessel is listing)
Today we tend to think of “inclinometers” as carpenters tools and “clinometers” in the context of surveying or scientific instruments. However, the nineteenth century meaning of the terms was exactly the opposite. Knight's comprehensive American Mechanical Dictionary , published in 1877, defined an inclinometer primarily as an instrument to detect the inclination in the earth's magnetic field, and gave as the best known example the “dipping needle”, a form of vertical compass widely used in mining. A secondary definition given was that of an instrument for measuring the slope of an embankment, incline, using a level attached to a “base piece which lies on the slope.”