Testing of the Basic Calibration

As an alternative to the approximation test according to Mandel, residual analysis [28] can be used for linearity testing. The residuals di are the vertical distances of the measuring values from the regression curve. 

For the graphical representation, it is practical to use the investigated working range as x-axis and the positively or negatively largest deviation as the intercept on the y-axis. If the mathematical model is correct, the residuals are normally distributed around the zero level. 

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