Note that rounding errors may occur, so always check the results.
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Do not use calculations for anything where loss of life, money, property, etc could result from inaccurate calculations.
Another version of the inch is also believed to have been derived from the width of a human thumb, where the length was obtained from averaging the width of three thumbs: a small, a medium, and a large one.
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The inch is usually the universal unit of measurement in the United States, and is widely used in the United Kingdom, and Canada, despite the introduction of metric to the latter two in the 1960s and 1970s, respectively.