Micro- is a unit prefix in the metric system denoting a factor of 10−6. Confirmed in 1960, the prefix comes from the Greek μ. 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 "μ" is not available; for example, "mcg" commonly denotes a microgram. Also the letter u instead of μ is allowed by one of the ISOdocuments. Examples:
The official symbol for the SI prefix micro- is a Greek lowercase mu. For reasons stemming from its design, there are two different characters in Unicode, which appear slightly different in some fonts, although most fonts use the same glyph. The micro sign is encoded in the "Latin-1 Supplement" range identical toISO/IEC 8859-1, at U+00B5, residing at this code point also in DEC MCS and ECMA-94. The Greek letter is encoded in the Greek range at U+03BC. According to The Unicode Consortium, the Greek letter character is preferred, 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, DIN 66030 and BS 6430 allow the prefix μ to be substituted by the letter u, as, for example, in um for μm, or uF for μF. Similar, capacitor values according to the RKM code defined in IEC 60062 , EN 60062, DIN 40825, BS 1852, IS 8186 etc. can be written as 4u7 instead of 4μ7 if the Greek letter μ is not available.
Other abbreviating conventions
In some health care institutions, house rulesdeprecate the standard symbol for microgram, "μg", in prescribing or chart recording, because of the risk of giving an incorrect dose because of the misreading of poor handwriting. The two alternatives are to abbreviate as "mcg" or to write out "microgram" in full. 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, and in physical sciences academia, "μg" remains the sole official abbreviation. In medical data exchange according to the Health Level 7 standard, the μ can be replaced by u as well.
