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

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

The prefixes myria- (ma or my, for 10000) and myrio- (mo, for 1/10000) came from the Greek μύριοι (mýrioi) 'ten thousand'. Part of the original metric system adopted by France in 1795, they were not retained when the SI prefixes were agreed internationally by the 11th CGPM in 1960.

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 myria-ton.

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).

Unofficial prefixes

There are many unofficial or fabricated metric prefixes circulating the internet, especially for values smaller than 10^-24 or larger than 10²⁴.^[1] One well-known unofficial prefix is bronto-, used in the fake term brontobyte. References on the World Wide Web suggest meanings of the bronto prefix to be variously any of 10¹⁵, 10²¹, 10²⁴, or 10²⁷. SI has already produced standard prefixes for 10¹⁵ (peta), 10²¹ (zetta) and 10²⁴ (yotta).^{[2][3][4][5][6]}

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-, udeko- and xenna-, weka-, vendeka-, udeka-, from Greek ennea-, deka-, endeka-, dodeka-; sometimes a t is added for greater differentiation, though both xento-, wekto- etc. and xenta-, wekta- etc. have been proposed.^[7]

See also

• SI prefix
• SI unit

References

1. ^ Final Answers: Measurement and Units Large table of units
2. ^ BBC article suggesting that a brontobyte is 10²⁷ bytes
3. ^ 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.)
4. ^ Article suggesting that a brontobyte is 10²¹ bytes
5. ^ Article suggesting that a brontobyte was 10¹⁵ bytes before the creation of the prefix peta- (Article is of dubious authority... suggests that Greek letters ν, π, and φ are SI prefixes for nano-, pico-, and femto-, instead of n, p, and f.)
6. ^ Article suggesting that brontobyte is 10²⁷ bytes
7. ^ "International System" in Glenn Elert, The Physics Hypertextbook

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.