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Micro-

Micro (Greek letter ? (U+03BC) or the legacy symbol µ (U+00B5)) is a unit prefix in the metric system denoting a factor of 10-6 (one millionth).[1] Confirmed in 1960, the prefix comes from the Greek (mikrós), meaning "small".

The symbol for the prefix is the Greek letter ? (mu). It is the only SI prefix which uses a character not from the Latin alphabet. "mc" is commonly used as a prefix when the character "?" is not available; for example, "mcg" commonly denotes a microgram. This is ambiguous, in that mcg could also be read as a micrigram, i.e. 10-14 g, the prefix micri is not standard, nor widely known, and considered obsolete. The letter u, instead of ?, is allowed by an ISO document.[2]

Examples
Prefix Base 10 Decimal English word Adoption[nb 1] Etymology
Name Symbol Short scale Long scale Language Derived word
yotta Y 1024 1000000000000000000000000 septillion quadrillion 1991 Greek eight[nb 2]
zetta Z 1021 1000000000000000000000 sextillion trilliard 1991 Latin seven[nb 2]
exa E 1018 1000000000000000000 quintillion trillion 1975 Greek six
peta P 1015 1000000000000000 quadrillion billiard 1975 Greek five[nb 2]
tera T 1012 1000000000000 trillion billion 1960 Greek four[nb 2], monster
giga G 109 1000000000 billion milliard 1960 Greek giant
mega M 106 1000000 million 1873 Greek great
kilo k 103 1000 thousand 1795 Greek thousand
hecto h 102 100 hundred 1795 Greek hundred
deca da 101 10 ten 1795 Greek ten
100 1 one -
deci d 10-1 0.1 tenth 1795 Latin ten
centi c 10-2 0.01 hundredth 1795 Latin hundred
milli m 10-3 0.001 thousandth 1795 Latin thousand
micro ? 10-6 0.000001 millionth 1873 Greek small
nano n 10-9 0.000000001 billionth milliardth 1960 Greek dwarf
pico p 10-12 0.000000000001 trillionth billionth 1960 Spanish peak
femto f 10-15 0.000000000000001 quadrillionth billiardth 1964 Danish fifteen, Fermi[nb 3]
atto a 10-18 0.000000000000000001 quintillionth trillionth 1964 Danish eighteen
zepto z 10-21 0.000000000000000000001 sextillionth trilliardth 1991 Latin seven[nb 2]
yocto y 10-24 0.000000000000000000000001 septillionth quadrillionth 1991 Greek eight[nb 2]
  1. ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.
  2. ^ a b c d e f Part of the beginning of the prefix was modified from the word it was derived from, ex: "peta" (prefix) vs "penta" (derived word).
  3. ^ The fermi was introduced earlier with the same symbol "fm", in which then the "f" became a prefix. The Danish word is used since it is vaguely spelled similar to fermi.

Symbol encoding in character sets

The official symbol for the SI prefix micro is a Greek lowercase mu (?).[4] For reasons stemming from its design, Unicode has two different character codes for the letter, which appear slightly different in some fonts, although most fonts use the same glyph. The micro sign (µ) is encoded in the "Latin-1 Supplement" range identical to ISO/IEC 8859-1 (since 1987), at U+00B5 (+),[5] residing at this code point also in DEC MCS (since 1983) and ECMA-94 (since 1985). The Greek letter (?) is encoded in the Greek range at U+03BC (+). According to The Unicode Consortium, the Greek letter character is preferred,[6] but implementations must recognize the micro sign as well. This distinction also occurs in some legacy code pages, notably Windows-1253.

In circumstances in which only the Latin alphabet is available, ISO 2955 (1974,[7] 1983[8]), DIN 66030 (Vornorm 1973;[9] 1980,[10][11] 2002[12]) and BS 6430 (1983) allow the prefix ? to be substituted by the letter u (or even U, if lowercase letters are not available), as, for example, in um for ?m, or uF for ?F. Similar, capacitor values according to the RKM code defined in IEC 60062 (IEC 62) (since 1952), EN 60062, DIN 40825 (1973), BS 1852 (1974), IS 8186 (1976) etc. can be written as 4u7 (or 4U7) instead of 4?7 if the Greek letter ? is not available.

Other abbreviating conventions

In some health care institutions, house rules deprecate the standard symbol for microgram, "?g", in prescribing or chart recording, because of the risk of giving an incorrect dose because of the misreading of poor handwriting.[13] The two alternatives are to abbreviate as "mcg"[13] or to write out "microgram" in full (see also List of abbreviations used in medical prescriptions). But this deprecation, focused on avoiding incorrect dosing in contexts where handwriting is often present, does not extend to all health-care contexts and institutions (for example, some clinical laboratories' reports adhere to it, whereas others do not[13]), and in physical sciences academia, "?g" remains the sole official abbreviation.

In medical data exchange according to the Health Level 7 (HL7) standard, the ? can be replaced by u as well.[14]

See also

References

  1. ^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived from the original (PDF) on 2017-08-14
  2. ^ ISO 2955, table 2.
  3. ^ Biology by Campbell & Reece, tenth edition. Ch. 6 "A Tour of the Cell". p. 98.
  4. ^ Prefixes of the International System of Units, International Bureau of Weights and Measures (page visited on 9 May 2016).
  5. ^ (Unicode 1.0, 1991)
  6. ^ Unicode Technical Report #25
  7. ^ ISO 2955-1974: lnformation processing - Representations of SI and other units for use in systems with limited character sets (1st ed.). 1974.
  8. ^ "Table 2". ISO 2955-1983: lnformation processing - Representations of SI and other units for use in systems with limited character sets (PDF) (2nd ed.). 1983-05-15. Retrieved . [1]
  9. ^ Vornorm DIN 66030 [Preliminary standard DIN 66030] (in German). January 1973.
  10. ^ DIN 66030: Darstellungen von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat (in German) (1st ed.). 1980.
  11. ^ "Neue Normen für die Informationsverarbeitung". Computerwoche (in German). 1981-01-09. Archived from the original on 2016-12-14. Retrieved .
  12. ^ DIN 66030:2002-05 - Informationstechnik - Darstellung von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat [Information technology - Representation of SI and other units in systems with limited character sets] (in German). Beuth Verlag [de]. May 2002. Retrieved .
  13. ^ a b c Burtis, Carl A.; Ashwood, Edward R.; Bruns, David E. (2012), Tietz Textbook of Clinical Chemistry and Molecular Diagnostics (5th ed.), ISBN 978-1455759422.
  14. ^ "Commonly Used UCUM Codes for Healthcare Units". HL7 Deutschland e.V. Retrieved .

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