DAVID R. FRAZIER / SCIENCE PHOTO LIBRARY DAVID R. FRAZIER / SCIENCE PHOTO LIBRARY
Spirit level. Construction worker using a spirit level to check that a wall is being built straight and not at an angle. This spirit level contains three yellow glass tubes, each containing liquid and a bubble. The glass tubes are orientated both horizontally and vertically, and have markings on them. This allows the spirit level to be used both to measure vertical surfaces, and horizontal ones. When the bubble stabilises between the markings on a glass tube, the wall or other surface is level. The construction worker is also holding a trowel, which he will use to add mortar to the wall as he builds more bricks onto it. The hard hat protects his head from injury.
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