Non-SI unit prefixes

There exist several unit prefixes that are used like the SI prefixes but are not part of the SI system.

Metric prefixes that were obsoleted or withdrawn from the SI standard

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 mesures).

Unofficial prefixes

There are many unofficial or fabricated metric prefixes circulating the internet, especially for values smaller than 10^-24 or larger than 10²⁴. 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).

See also

References

External links

• Moerner Lab Single-Molecule Research Page (Jokingly defines 1 guacamole = 1 / (Avocado's number) of moles. Scientific paper with reference)

Related articles

• SI prefix
• SI unit