ИМХО, давно это дело известно.
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SAND'S LEVELS
"Julius Sand, the inventor of Sand's Levels, was a practical bricklayer. Back in the 1890's he conceived the idea of the combination level and plumb, to which he later added the idea of the boxed-in type of protective glass. In 1895 he invented the Sands type of "solid-set" non-adjustable levels. Sands originated the aluminum type level to offer a light weight for the market. Here was laid the foundation for what today is one of the largest level manufacturing businesses in the world."
"Today, Sands enjoys and carefully guards the enviable reputation expressed in their slogan: Sands Levels Tell the Truth."