Quickly calculate the standard deviation of a list of numbers.

In statistics the standard deviation (SD) (represented by the Greek letter sigma σ) is a measure that is used to quantify the amount of variation or dispersion of a set of data values. A low standard deviation indicates that the data points tend to be very close to the mean (also called the expected value) of the set while a high standard deviation indicates that the data points are spread out over a wider range of values.