In ancient times, humans and other fields to measure the length measurement has been carried out, initially on the hand, foot, etc., as the unit of length. But the human hand, foot sizes, in the commodity exchange in the difficulties encountered, so they appeared to object as the unit of measurement, such as 2400 BC, the ancient Egyptian cubit there, the Chinese Shang Dynasty ivory appeared nine feet and AD manufactured in such Xinmang brass caliper.
5,000 years ago, ancient Egypt the Nile flood every year, flooding large tracts of land, covered with soil brought by the flood in the fields, so that does not recognize the original field boundaries, so every time after the flood receded, people will re-measure land, so have the first geometry.
There are many ways measurements length, with hands, feet and so on. However, these methods do not need very precise measurements to use. Currently, the world's leading length with a variety of scales to measure. Common scale with a ruler, vernier caliper and measuring tape, etc.. Caliper suitable for measuring the general scale difficult to measure the round items, the part diameter, thickness and so on. High precision. Length of the unit of measurement is m, denoted by M. In 1978, French regulations: the distance between the Earth's Arctic and Antarctic one ten-millionth the length of one meter. Through the promotion of this provision, is now internationally accepted as the unit of length.
Measuring according to their use can be divided into three categories:
1, the standard measuring tool. Refers to the testing standards used to measure or measuring tool. Such as gauge blocks, multi-faceted prism, the surface profile comparators and so on.
2, common measuring tool (or universal measuring tool.) Generally refers to a unified manufacturing plant by the gauge of measuring universal. Such as a ruler, flat, angle blocks, calipers and so on.
3, special measuring tools (or non-standard measuring tools). Parts exclusively for testing the parameters of a technology design and manufacture of measuring tools. Such as outside the groove caliper, steel wire rope caliper, step away from the gauges.
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