development of levelsThe tool for determining horizontal direction is called a level. The Egyptians used an A-frame, on which a plumb line was suspended from the vertex of the A. When the feet of the A were set on the surface to be checked, if the plumb line bisected the crossbar of the A, the surface was horizontal. The A-frame level was used in Europe until the middle of the 19th century. Sometimes a variation is...
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