In measurement, which Greek letter is applied to the prefix micro-, equal to 10-6?
Micro- Micro- Micro- (Greek letter μ or legacy micro symbol µ) is a unit prefix in the metric system denoting a factor of 10 (one millionth). Confirmed in 1960, the prefix comes from the Greek (""), meaning "small". The symbol for the prefix comes from the Greek letter μ (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 "μ" is not available; for example, "mcg" commonly denotes a microgram. Also the letter u instead of μ is allowed by one of the ISO documents.
Metric prefix has a symbol that is used in combination with the symbols for units of measure. For example, the symbol for "kilo-" is 'k', and is used to produce 'km', 'kg', and 'kW', which are the SI symbols for kilometre, kilogram, and kilowatt, respectively. Where the Greek letter 'μ' is unavailable, the symbol for micro 'µ' may be used. Where both variants are unavailable, the micro prefix is commonly written as the lowercase Latin letter 'u'. Prefixes corresponding to an integer power of one thousand are generally preferred. Hence "100 m" is preferred over "1 hm" (hectometre) or "10 dam" (decametres).