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Spirit level

Spirit level

A spirit level, bubble level or simply a level is an instrument designed to indicate whether a surface is horizontal (level) or vertical (plumb). Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in some photographic or video graphic work.

Early spirit levels had banana-shaped curved glass vials at each viewing point. These vials are half filled with a liquid, usually a coloured spirit or alcohol, which leaves a bubble in the tube. They have a slight upward curve, so that the bubble naturally rests in the centre, the highest point. At slight inclinations the bubble travels away from the marked centre position. Where a spirit level must also be usable upside-down or on its side, the banana-shaped tube is replaced by a barrel-shaped tube.

Alcohols such as ethanol are often used rather than water. Alcohols have low viscosity and surface tension, which allows the bubble to travel the tube quickly and settle accurately with minimal interference with the glass surface. Alcohols also have a much wider liquid temperature range, and won't break the vial as water could due to ice expansion. A colourant such as fluorescein which is usually yellow or green, may be added to make it easier to see the bubble.

Before using a spirit level, always check that is accurate. Always handle the spirit level carefully, dropping it or not treating it carefully can make it lose its accuracy. Make sure the spirit level gets cleaned after use so that there is no sand or cement on it.