Levels are used to find out whether an object is level to another reference point. A hand level is a level that is small enough to fit in the user’s hand. This is in contrast to stationary levels, such as those used by surveyors, that require tripods or mounting to function. The most common form of hand level is called a spirit level, and it determines whether an object is level in relation to gravity.
Levels all orient on something to find if something else is level in relation. Most hand levels operate based on the object's relation to gravity. Essentially, they see if the checked surface is perpendicular to straight down. Levels that are more complex can check surfaces in relation to other objects and directions. These tasks are often too difficult for a simple hand level.
Spirit levels are the most common form of hand level in use. These levels look like small tubes or platters with a bubble in them. The bubble moves along the tube to show the levels' relationships to down. They are called spirit levels because they are typically filled with an artificially-colored alcohol, such as ethanol, in order to let the bubble move more freely.
There are two main designs for spirit levels: platters and tubes. The platter style level is a round container filled with alcohol that is meant to be looked down upon. When the user looks down at the top of the level, there is a series of circles giving the level an appearance similar to a bull’s eye. There is also a bubble that floats freely within the liquid. A tube-style hand level simply has a small tube that sits parallel to the ground; it also has a free-floating bubble and a series of markings.
The bubble sits in the center of the tube or platter when the level is perpendicular to gravity. A tube level measures the slope underneath it in two directions, the axis of the tube. The platter style measures in four directions, basically a plus sign axis. In both cases, the additional lines on the measuring surface help the user see exactly how close the bubble is to the center or how close the surface is to level.
In recent years, an electronic version of the spirit level has come on the market. These devices contain two small tubes inside a plastic housing. The device measures the positions of the materials inside these tubes and displays the exact angle of the surface underneath. Even though they are much more accurate, the simplicity and low cost of the common spirit level keeps them the most popular style of hand level.