Nanometre, Length
10−9, nanometre, nm. The symbol for metre is m. Decimal multiples and submultiples of the metre, such as kilometre (1000 metres) and centimetre (1/100 metre), are indicated by adding SI prefixes to metre. Read more 
In general English usage, length (symbols: l, L) is one particular instance of distance: an object's length is its extent along its longest dimension. This is to be contrasted with height, denoting vertical extent, and width (or breadth), denoting a lateral extent along a dimension shorter than an object's length. In the physical sciences and engineering, the word "length" is typically used synonymously with "distance".
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