Residual standard deviation

The residual standard deviation (sometimes referred to as the root mean square error) is calculated using the following formula:

d = 3	Degree of freedom for a quadratic curve, no forced origin
d = 2	Degree of freedom for a quadratic curve with forced origin, or Degree of freedom for a linear curve, no forced origin
d = 1	Degree of freedom for a linear curve with forced origin
ResidualStdDev	Residual standard deviation
yi	Measured response (Area, AreaRatio (ISTD method), Height or HeightRatio (ISTD method)) or amount (Amount, AmountRatio (ISTD Method)), depending on calibration mode
Yi	Predicted response or amount (using the calibration curve)
n	number of calibration points

For Include origin calibration curve types, the origin (0,0) is included as a regular point in the calculation and counted by n.

The y values are not weighted.

The residual standard deviation gives a more sensitive measure of the curve quality than does the correlation coefficient. For a perfect fit, the residual standard deviation is zero. With increasing residual standard deviation values, the calibration points get further away from the curve.