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The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of 1 / 299 792 458 of a second, where the second is defined by a hyperfine transition frequency of caesium.
The base unit in the International System of Units (SI) is the meter, defined as "the length of the path travelled by light in vacuum during a time interval of 1 ⁄ 299792458 seconds." [ 9 ] It is approximately equal to 1.0936 yd .
The metre, symbol m, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299 792 458 when expressed in the unit m⋅s −1, where the second is defined in terms of the caesium frequency Δν Cs. The concept of defining a unit of length in terms of a time received some comment. [134]
The micrometre (SI symbol: μm) is a unit of length in the metric system equal to 10 −6 metres ( 1 / 1 000 000 m = 0. 000 001 m). To help compare different orders of magnitude , this section lists some items with lengths between 10 −6 and 10 −5 m (between 1 and 10 micrometers , or μm).
The SI comprises a coherent system of units of measurement starting with seven base units, which are the second (symbol s, the unit of time), metre (m, length), kilogram (kg, mass), ampere (A, electric current), kelvin (K, thermodynamic temperature), mole (mol, amount of substance), and candela (cd, luminous intensity). The system can ...
metre: m length "The metre, symbol m, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299 792 458 when expressed in the unit m s −1, where the second is defined in terms of ∆ν Cs." [1]
The prefix symbols are always prepended to the symbol for the unit without any intervening space or punctuation. [9] This distinguishes a prefixed unit symbol from the product of unit symbols, for which a space or mid-height dot as separator is required. So, for instance, while 'ms' means millisecond, 'm s' or 'm·s' means metre-second.
In the International System of Units (SI), the base unit of length is the metre (symbol, m), now defined in terms of the speed of light (about 300 million metres per second). The millimetre (mm), centimetre (cm) and the kilometre (km), derived from the metre, are also commonly used units.