A spirit level is used to determine that a surface is level. The level itself usually consists of plastic tubing encased within a ruler or level-measuring instrument. The tubing centre is marked with lines, and the tube is incompletely filled with liquid. This leaves an air bubble. As one rotates the spirit level, the bubble will move up and down the scale. When the bubble rests in the centre of the scale - between the marker lines - one knows that the surface is level. Or that one is holding the spirit level, level. The tool is moderately worthy in that it is essential to a flat, level, level surface.
One may attach the level to a surface with clamps if desired, and then move the surface until level. Some spirit levels contain vertical horizontal and diagonal levels to measure each axis. This can be useful, for example, in checking the levels of a supposedly 90 degree angle. In this case one will see that the corner is accurate if the level displays that both horizontal and vertical are level.
Types of Spirit Levels
Levels may be encased in a horizontal bar analogous to a ruler, such as the carpenter's level. They can also be hung on string, to check that the string line is level. Some machines will have a level built in also, to ensure accurate level surfaces.