The "Linear Through Zero" curve fit type does not calculate an R^2 value in UNIFI - WKB90631

SYMPTOMS

• Processing a results set with the "Linear Through Zero" calibration curve fit type does not calculate the calibration R² value

• If the curve fit is changed to "Linear", R² is calculated

ENVIRONMENT

• UNIFI

CAUSE

Consider the linear curve fit type; the calculation of R² is based on a comparison of the Residual Sum of the Squares to the Sum of Squares about the Regression and the Mean Sum of Squares. When R² approaches 1, the regression model accounts for most of the variance of the calibration data, the Residual Sum of Squares is small compared with the Mean Sum of Squares, and the R² is reported. When the calibration is linear forced through zero, it is possible for the Residual Sum of Squares to be much larger than the Mean Sum of Squares when the range of Y values is small. In such cases, R² is not reported.
This is not a defect. By design, no R² value is reported when a through-zero curve type is used.

FIX or WORKAROUND

Select a "Linear" curve fit that does not go though the zero point of the axes.

ADDITIONAL INFORMATION