The Range Method is a method for estimating the standard deviation that is used in Statistical Process Control and Measurement Systems Analysis. It uses the equation:
s 
process standard deviation 

mean of the ranges of a number of samples 
d_{2} 
a constant obtained from tables 
Normally 30 or more samples should be used. Some of the methods used in Measurement Systems Analysis use 15 samples or less and in this case the equation is modified to:
