Level is an instrument used by carpenters, plumbers, and others to determine if a surface is perfectly horizontal. Most levels consist of a small, arched glass tube set in a bar of wood or metal. The tube is marked at its center, which is its highest point. It contains alcohol or another liquid and a bubble of air. When a level is placed lengthwise on a perfectly horizontal surface, the bubble rests at the center of the tube. If the surface being checked is tilted, the bubble rises to the high end of the tube. Some levels have additional tubes that are set at right angles to the length of the tool. These tubes enable workers to tell if a surface is plumb (vertical).
Levels generally derive their names from their use. For example, mason’s levels are used by masons in building walls of brick or stone. These levels measure 4 feet (1.2 meters) long and are the longest levels. A carpenter’s level is similar to a mason’s level, but is commonly about 2 feet (60 centimeters) long. Line levels, sometimes called string levels, are hung along a tight line or string. Builders use them in laying foundations and in performing other work that involves leveling long spans. Line levels, which are about 3 inches (8 centimeters) long, are the shortest levels.
A builder’s level contains a telescope and a leveling tube mounted on a tripod (three-legged stand). It is used to measure horizontal angles. A similar level, called a transit, measures vertical and horizontal angles. These levels enable builders, engineers, and surveyors to measure angles and level buildings with great accuracy.
