Three Sigma (`3 sigma`) is the percentage of a data set whose values fall within three standard deviation of the data set's mean. Low variation indicates data tend to be close to the mean. In project management the number of sigma cited is used to gauge the quality of a process, where lesser variation indicates fewer errors or failures. This fraction is represented here as a decimal fraction conveying that 99.73% of the data falls with three standard deviation from the mean of the data set.