# What is the sign of Sigma?

## What is the sign of Sigma?

The symbol Σ (sigma) is generally used to denote a sum of multiple terms. This symbol is generally accompanied by an index that varies to encompass all terms that must be considered in the sum.

## What does μ mean?

Micro-

**Why is Sigma used?**

Sigma is the 18th letter of the Greek alphabet and is equivalent to our letter ‘S’. In mathematics, the upper case sigma is used for the summation notation. The lower case sigma stands for standard deviation. Neither of them looks like our letter ‘S’, but they are both the Greek equivalent of it.

**What does 3 sigma represent?**

The term “three-sigma” points to three standard deviations. Shewhart set three standard deviation (3-sigma) limits as a rational and economic guide to minimum economic loss. On a bell curve, data that lie above the average and beyond the three-sigma line represent less than 1% of all data points.

### What is a good sigma level?

A process with 50% defects (DPMO = 500,000) would have a Sigma Level of 0. Usually, a process with a Sigma Level of 6 or greater is usually considered as an excellent process.

### What is a sigma value?

A sigma value is a statistical term otherwise known as a standard deviation. Sigma is a measurement of variability, which is defined by the Investor Words website as “the range of possible outcomes of a given situation.” Add a set of data and divide by the number of values in the set to find the mean.