Non-SI unit prefixes

A number of unit prefixes, similar to the standardized SI prefixes, have been used or proposed by various sources, but which are not part of the International System of Units (SI).

Former metric prefixes

Distance marker on the Rhine: 36 (XXXVI) myriameters from Basel

Some prefixes were used in older versions of the metric system but are not part of the modern metric system, the SI.

The prefix myria, ^{[1] [2]} denoting a factor of 10000, originated from the Greek μύριοι (mýrioi), that is, myriad, for ten thousand, and the prefixes demi- and double-, denoting a factors of 1/2 and 2 respectively,^[3] were parts of the original metric system adopted in France in 1795, but they were not retained when the SI prefixes were agreed internationally by the 11th CGPM conference in 1960. They were dropped because they were not decimal, nor symmetrical. They were rarely used, though the myriameter (10 km) is occasionally encountered in 19th-century train tariffs, or in some classifications of wavelengths as the adjective myriametric. In Sweden (and possibly elsewhere), the myriameter is still very common in everyday use (although not recognized or used officially). In Swedish this unit is called 'mil', sometimes causing confusion when Swedes use the English word 'mile' (incorrectly) as a direct translation. Of units customarily used in trade in France, the myriagramme (10 kg) was the metric replacement for an avoirdupois unit, the quarter (25 pounds). (see also myriogramme, a genus of seaweed). In Isaac Asimov's novel Foundation and Empire, there is a mention of the myriaton.

Also obsolete are metric double prefixes, such as those formerly used in micromillimetres (now nanometres), micromicrofarads (now picofarads), hectokilometres (also in the derived adjective hectokilometric typically used for qualifying the fuel consumption measures).^[4]

Unofficial prefixes

There are many unofficial or fabricated metric prefixes circulating the internet, especially for values smaller than 10⁻²⁴ or larger than 10²⁴. ^{[5] [6]} One unofficial prefix is bronto-, which has been used in the term brontobyte to represent anything from 10¹⁵ to 10²⁷ bytes.^{[7][8][9][10][11]} SI has already produced standard prefixes for 10¹⁵ (peta), 10²¹ (zetta) and 10²⁴ (yotta).

The z and y on the extreme prefixes zepto-, yocto- and Zetta-, Yotta- suggest the start of a series backwards through the alphabet. Following the initial letters are distorted Greek numerals (h)epta- and octa-. This pattern has been extended further, with the terms xenno-, weko-, vendeko- and xenna-, weka-, vendeka- from Greek ennea-, deka-, endeka-; sometimes a t is added for greater differentiation, though both xento-, wekto- etc. and xenta-, wekta- etc. have been proposed.^[12] An internet petition has lobbied for the usage of the prefix "hella-" for 10²⁷, a movement that began on the campus of UC Davis.^[13]

Other proposed prefixes

omni- (Om) 10¹⁰⁰⁰

Centili- (Cen) 10⁶⁰⁰ (highest lexicographically accepted named number in the system of successive powers of ten as the centillion, first recorded in 1852, in European traditional usage; alternatively it can be 10³⁰³ in U.S. and Canadian usage)

Googol- (Goo) 10¹⁰⁰ (highest known power accepted in Western Scientific field)

Asankhyeya- (Asa-) 10¹⁴⁰ (highest number outside the decimal notation of the Buddhist work of Jain in 100 BC)

lako- (l) 10⁵ (Indian English lakh, lac 'hundred-thousand', from Pali [lakʰ])

ribo- (r) 10⁴ (Hebrew ribo 'ten-thousand', from highest Aramaic number)

myri- (my) 10⁻⁴ (modifying the discontinued metric prefix myrio- 'ten-thousandth', from Latin myrias 'ten-thousand', from Greek murioi)

mini- (mi) 10⁻⁴ (Latin minimus, 'smallest', the superlative of parvus 'small')

yi- (y) 10⁻⁵ (Chinese yì 'hundred-thousand')

tini- (ti) 10⁻⁵ (Middle English tine 'tiny')

angstro- (å) 10⁻¹⁰ (from metric angstrom, 10⁻¹⁰ meters)

Japanese large numbers

oku 10⁸

kei 10¹⁶

gai 10²⁰

jō 10²⁸

kō 10³²

sei 10⁴⁰

sai 10⁴⁴

goku 10⁴⁸

gōgasha 10⁵²

asōgi 10⁵⁶

nayuta 10⁶⁰

fukashigi 10⁶⁴

muryōtaisū 10⁶⁸

Chinese large numbers

wàn 10⁴ A group for ten thousand.

yì 10⁵

jīng 10⁷

ráng 10¹⁰

gōu 10¹¹

zhēng 10¹³

zài 10¹⁴

Large numbers from Buddhism found in Chinese numerals

See also: Chinese numerals

jí 10⁴⁸

héng hé shā 10⁵² Literally means "Sands of the Ganges"; a metaphor used in a number of Buddhist texts referring to the grains of sand in the Ganges River.

ā sēng qí 10⁵⁶ From Sanskrit Asaṃkhyeya

nà yóu tā 10⁶⁰ From Sanskrit Nayuta

bùkě sīyì 10⁶⁴ Literally translated as "unfathomable".

wú liàng 10⁶⁸ Literally translated as "without measure"

dà shù 10⁷² Literally translated as "a large number"

Japanese small numbers

sen 10⁻⁷

sha 10⁻⁸

Small numbers from Chinese numerals

These have fallen into disuse by the Chinese.

miǎo 10⁻¹¹ (Ancient Chinese)

āi 10⁻¹⁰ (Ancient Chinese) A good alternative for angstrom.

shā 10⁻⁸ (Ancient Chinese)

qiān 10⁻⁷ (Ancient Chinese)

hū 10⁻⁵ (Ancient Chinese)

sī 10⁻⁴ (Ancient Chinese)

Other possible prefixes without a set factor higher than exa

Super- (Su-)

Uni- (U-) In reference to Universe.

Ultra- (Ul-)

Supra- (S-)

Macro- (Ma-)

IEC binary prefixes

Owing to the frequent ambiguous and confusing use of standard SI prefixes in the information technology field^[14] to represent unit multiples of powers of two, rather than powers of ten (e.g., the use of kilo for 2¹⁰=1024, rather than 1000), the International Electrotechnical Commission introduced a set of new, but similarly named, binary prefixes to be used for such purposes (e.g., kibi for 2¹⁰=1024). These units have been accepted and recommended by all international standards bodies.

See also

• SI unit

References

1. ^ 29th Congress of the United States, Session 1 (1866-05-13). "H.R. 596, An Act to authorize the use of the metric system of weights and measures". http://lamar.colostate.edu/~hillger/laws/metric-act-bill.html. 
2. ^ D. Brewster (1830). The Edinburgh Encyclopaedia. p. 494. http://books.google.com/books?id=h6miHpDMjXEC&pg=PA494. 
3. ^ histoire.du.metre.free.fr
4. ^ Rowlett, Russ (2010-05-28). "millimicro-". How Many? A Dictionary of Units of Measurement. http://www.unc.edu/~rowlett/units/dictM.html. Retrieved 2010-10-30. 
5. ^ Gerard P. Michon. "Current and Deprecated Prefixes". http://www.numericana.com/answer/units.htm#prefix. 
6. ^ Gerard P. Michon. "Funny prefixes & dubious proposals (updated yearly)". http://www.numericana.com/answer/humor.htm#prefixes. 
7. ^ BBC article suggesting that a brontobyte is 10²⁷ bytes
8. ^ Sybase article suggesting that a brontobyte is 10²⁴ or 10²⁷ bytes (Note article's table a few pages down. Note also it mistakenly places 1 terabyte = 1,000 megabytes. It should be 1 terabyte = 1,024 gigabytes. Also yottabyte is shown incorrectly as zottabyte. With those corrections, it also is clearly 10²⁷.)
9. ^ Article suggesting that a brontobyte is 10²¹ bytes
10. ^ Article suggesting that brontobyte is 10²⁷ bytes
11. ^ "Article suggesting that a brontobyte is 10¹⁵ bytes". MacUser 7: 362. 16 February 1991. http://books.google.com/books?id=j31VAAAAMAAJ&q=brontobyte. "1 brontobyte (1,000,000,000 megabytes)" 
12. ^ "International System" in Glenn Elert, The Physics Hypertextbook
13. ^ "Hellabytes? A Campaign to Turn Slang into Science". Time. 2010-03-10. http://www.time.com/time/health/article/0,8599,1970849,00.html. Retrieved 2010-05-20. 
14. ^ Prefixes for binary multiples at International Electrotechnical Commission

External links

• Moerner Lab Single-Molecule Research Page (Jokingly defines 1 guacamole = 1 / (Avocado's number) of moles. Scientific paper with reference)
• Vendeka.org Home page for the use of the non-SI prefix vendeka to represent 10 to the power of 33, as in vendekabyte.