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The millimetre (International spelling as used by the International Bureau of Weights and Measures; SI unit symbol mm) or millimeter (American spelling) is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit
SI base unit
of length. Therefore, there are one thousand millimetres in a metre. There are ten millimetres in a centimetre. One millimetre is equal to 7003100000000000000♠1000 micrometres or 7006100000000000000♠1000000 nanometres. A millimetre is equal to exactly ​5⁄127 (approximately 0.039370) of an inch.

Contents

1 Definition 2 Unicode
Unicode
symbols 3 Measurement 4 See also 5 References

Definition[edit] Since 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of 1/7008299792458000000♠299792458 of a second".[1] A millimetre, 1/1000 of a metre, is therefore the distance travelled by light in 1/7011299792458000000♠299792458000 of a second. Unicode
Unicode
symbols[edit] For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode
Unicode
has symbols for:

millimetre (㎜) - code U+339C[2] square millimetre (㎟) - code U+339F[2] cubic millimetre (㎣) - code U+33A3[2]

In Japanese typography, these square symbols were historically used for laying out unit symbols without distorting the grid layout of text characters. Measurement[edit] On a metric ruler, the smallest measurements are normally millimetres.[3] High-quality engineering rules may be graduated in increments of 0.5 mm. Digital Vernier callipers are commonly capable of reading increments as small as 0.01 mm.[4] Microwaves with a frequency of 300 GHz have a wavelength of 1 mm. Using wavelengths between 30 GHz and 300 GHz for data transmission, in contrast to the 300 MHz to 3 GHz normally used in mobile devices, has the potential to allow data transfer rates of 10 gigabits per second.[5] The smallest distances the human eye can resolve is around 0.02 to 0.04 mm, approximately the width of a human hair.[6] A sheet of paper is typically between 0.07 mm and 0.18 mm thick, with ordinary printer paper or copy paper approximately a tenth of a millimetre thick.[7] See also[edit]

Look up millimetre in Wiktionary, the free dictionary.

Metric system Orders of magnitude (length) Submillimeter

References[edit]

^ "17th General Conference on Weights and Measures (1983), Resolution 1". International Bureau of Weights and Measures. Retrieved 3 December 2013.  ^ a b c " CJK Compatibility" (PDF). unicode.org. Retrieved 3 December 2013.  ^ "How do I read a ruler?". onlineconversion.com. Retrieved 3 December 2013.  ^ "Accuracy of Calipers". TresnaInstrument.com. Retrieved 3 December 2013.  ^ Huang, Kao-Cheng; Wang, Zhaocheng (2011). Millimeter Wave Communication Systems. ISBN 9781118102756.  ^ "How Small Can the Naked Eye See?". Focus Magazine. Retrieved 3 December 2013.  ^ "Thickness of a Piece of Paper". hypertextbook.com. Retrieved 3 December 2013. 

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SI units of length

From smallest to largest (left to right). Commonly used units shown in bold italics.

yoctometre (1×10−24 m) zeptometre attometre femtometre picometre nanometre micrometre millimetre centimetre decimetre metre (m) decametre hectometre kilometre megametre gigametre terametre petametre exametre zettametre yott

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