Introduction to Least Squares Method of Best Fit
Standard Error of Estimate
The sum of squares of the deviations can also be used to provide an estimate of how closely the data cluster around the line. The Standard Error of Estimate (Se) is one such estimate, and is calculated according to the following formula, where S denotes summation, and the yi and 
i are the observed and theoretical y-values of the datapoints, respectively:
For example, the Standard Error of Estimate of the preceding example is the following:
