VICTOR DE SCHWANBERG / SCIENCE PHOTO LIBRARY VICTOR DE SCHWANBERG / SCIENCE PHOTO LIBRARY
Spirit levels. Close-up of three spirit levels in the primary colours of red, green and blue. A spirit level is used to measure how level a surface is. It consists of a tube filled with a coloured fluid (usually yellow) and a single air bubble. When the spirit level is placed on an even, flat surface, the air bubble will remain between the two vertical lines in the centre of the tube (as here). However, if the surface slopes, the air bubble will move to the left or right of the markings.
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