Levels were used mainly in the construction trades to build houses, railroads, bridges, or anything else that needed to be made level to the ground. Machinist levels were used to ensure lathe beds were level, and sighting levels helped determine the rise or fall of slope over a given distance. By far the most common type of level is the bubble level, which uses a air bubble in water or thin oil to show deviation from horizontal. But other clever devices were also used to measure inclinivity (slope), and levels with these devices are called inclinometer levels. Levels come in all sizes from tiny machinist levels to large railroad levels.