Q. Why is it called a spirit level?

Answer

"Spirit levels" "bubble levels" "levels" and "spirits" are all names for the same tool used frequently in the building trade. Most spirit levels consist of a tube and a holder; the tube can be made of glass or plastic and the holder might be made of plastic wood aluminum or some other metal. If the bubble within a spirit level is centered as opposed to off to one side the platform or item sitting parallel to the spirit will be level and the one sitting perpendicular to the spirit will be aligned vertically. To test a spirit level's accuracy spin it 180° on the same surface and measure the bubble increment.