| 词条 | Millimetre |
| 释义 |
| bgcolor = | name = Millimetre | image = Ruler with millimeter and centimeter marks.png | caption = Ruler with millimetre and centimetre marks | standard = SI derived unit | quantity = Length | symbol = mm | namedafter = The metric prefix mille (Latin for "one thousand") and the metre | units1 = micrometres | inunits1 = {{val|1|e=3|ul=μm}} = 1000 μm | units2 = centimetres | inunits2 = {{val|1|e=-1|}} cm = 0.1 cm | units3 = metres | inunits3 = {{val|1|e=-3|}} m = 0.001 m | units4 = kilometres | inunits4 = {{val|1|e=-6|ul=km}} | units5 = inches | inunits5 = {{convert|1|mm|in|disp=out|lk=on|sigfig=5|comma=gaps}} | units6 = feet | inunits6 = {{convert|1|mm|ft|disp=out|lk=on|sigfig=5|comma=gaps}} }} 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 of length. Therefore, there are one thousand millimetres in a metre. There are ten millimetres in a centimetre. One millimetre is equal to {{val|1000}} micrometres or {{val|1,000,000}} nanometres. A millimetre is equal to exactly {{frac|5|127}} (approximately 0.039370) of an inch. DefinitionSince 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of {{sfrac|{{val|299,792,458}}}} of a second".[1] A millimetre, {{sfrac|1000}} of a metre, is therefore the distance travelled by light in {{sfrac|{{val|299,792,458,000}}}} of a second. Informal TerminologyA common shortening of millimetre in spoken English is "mil". This can cause confusion since in the United States, "mil" traditionally means a thousandth of an inch. Unicode symbolsFor the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for:
In Japanese typography, these square symbols were historically used for laying out unit symbols without distorting the grid layout of text characters. MeasurementOn a metric ruler, the smallest measurements are normally millimetres.[3] High-quality engineering rules may be graduated in increments of 0.5 mm. Digital 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{{Wiktionary|millimetre}}
References1. ^{{cite web |url=http://www.bipm.org/en/CGPM/db/17/1/ |title=17th General Conference on Weights and Measures (1983), Resolution 1. |accessdate=3 December 2013 |publisher=International Bureau of Weights and Measures}} {{SI units of length}}2. ^1 2 {{cite web |url=https://www.unicode.org/charts/PDF/U3300.pdf |title=CJK Compatibility |publisher=unicode.org |accessdate=3 December 2013}} 3. ^{{cite web |url=http://www.onlineconversion.com/faq_05.htm |title=How do I read a ruler? |publisher=onlineconversion.com |accessdate=3 December 2013}} 4. ^{{cite web |url=http://www.tresnainstrument.com/accuracy_of_calipers.html |title=Accuracy of Calipers |publisher=TresnaInstrument.com |accessdate=3 December 2013}} 5. ^{{cite book |url=https://books.google.com/books?id=kCmyPdxme1AC&lpg=PP1&pg=PP15#v=onepage&q&f=false |title=Millimeter Wave Communication Systems |isbn=9781118102756 |last1=Huang |first1=Kao-Cheng |last2=Wang |first2=Zhaocheng |year=2011}} 6. ^{{cite web |url=http://sciencefocus.com/qa/how-small-can-naked-eye-see |title=How Small Can the Naked Eye See? |publisher=Focus Magazine |accessdate=3 December 2013}} 7. ^{{cite web |url=http://hypertextbook.com/facts/2001/JuliaSherlis.shtml |title=Thickness of a Piece of Paper |publisher=hypertextbook.com |accessdate=3 December 2013}} 3 : Units of length|Orders of magnitude (length)|1000 (number) |
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