Smart tools level

A spirit level, 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 some photographic or videographic work.

Early spirit levels had very slightly curved glass vials with constant inner diameter at each viewing point. These vials are incompletely filled with a liquid, usually a colored spirit or alcohol, leaving a bubble in the tube. They have a slight upward curve, so that the bubble naturally rests in the center, the highest point. At slight inclines the bubble travels away from the marked center position. Where a spirit level must also be usable, the curved constant-diameter is replaced by an uncurved barrel-shaped tube with a slightly larger diameter in its middle.

Alcohols such as ethanol are often used rather than water. Alcohols have low viscosity and surface tension, which allows the bubble to travel quickly and accurately with minimal interference with the glass surface. Alcohols also have a much wider liquid temperature range, and will not break the vial as water could due to ice expansion. A colorant such as fluorescein, typically yellow or green, may be added to increase the visibility of the bubble.

An extension of the spirit level is the bull's eye level: a circular, flat-bottomed device with the liquid under a slightly convex glass with a circle at the center. It serves to level a surface across a plane, while the tubular level is only in the direction of the tube.