A spirit level is a tool designed to determine whether a surface is absolutely horizontal or vertical. A horizontal surface is called a level surface and a vertical surface is called a plumb surface. All sorts of professions utilize spirit levels, including: bricklayers, stonemasons, surveyors, metalworkers, carpenters, and more. The way spirit levels work is that the container of the level is filled just slightly less than full, leaving a bubble of air that travels around the container depending upon its positioning. The container has a slight curve upwards allowing the bubble to naturally rest at the center. Additionally, each spirit level has a center marker denoting the precise middle of the container. Then, when you rest the spirit level on a surface, you can tell whether there are any inclinations in the design that need to be adjusted. The liquid inside of a spirit level is more commonly an alcohol, rather than just water. This is because alcohol allows the air bubble to move about the tube more quickly and to settle with less interference from the container, due to its low viscosity and low surface tension. Spirit levels are simple little tools that are incredibly useful for precision measurement and accuracy.