A spirit level or bubble 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 videographic work.
Original spirit levels had two banana-shaped curved glass vials at each viewing point and were much more complicated to use. In the 1920s, Henry Ziemann invented the modern level with a single vial. These vials, common on most ordinary levels today,...