**Length - Wikipedia**
https://en.wikipedia.org/wiki/Length

In the physical sciences and engineering, when one speaks of units of length, the word length is synonymous with distance. There are several units that are used to measure length. Historically, units of length may have been derived from the lengths of human body parts, the distance traveled in a number of paces, the distance between landmarks or places on the Earth, or arbitrarily on the length of some common object. In the International System of Units (SI), the base unit of length is the metre(symbol, m) and is now defined in ter…

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