Sigma
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Sigma may refer to many things:
- Sigma (upper case Σ, lower case σ, alternative ς) is a letter in the Greek alphabet. See Sigma (letter).
- The upper-case letter Σ is used as a symbol for the summation operator forming a series in mathematics.
- The upper-case letter Σ is used as a symbol for a certain alphabet of a language, or of some other object dependent on an alphabet; expressed in mathematical terms, eg "the language defined by alphabet Σ={a,b,c} and the rules ..."
- The lower-case letter σ is used as a symbol for the standard deviation of a population in statistics.
- The lower-case letter σ is used as a symbol for the divisor function in number theory.
- The lower-case letter σ is used as a symbol for the Stefan-Boltzmann constant of radiation in physics.
- sigma1 and sigma2 are cell receptors in biochemistry and pharmacology.
- The lower-case letter σ is used as a symbol for the Sigma factor of RNA polymerase in biology.
- Sigma is the name of the main villain from the video game series Mega Man X.
- Sigma Corporation is a manufacturer of cameras, lenses and camera accessories.
- A model of handgun manufactured by Smith and Wesson.
- A series of sailing yachts.
- The Mitsubishi Motors Corporation car known as the Mitsubishi Sigma (variant of world-wide released Mitsubishi Galant).
- SIGMA is Nielsen Media Research's tracking system that allows Nielsen to electrionically monitor airplay of videos.