Two approaches to obtain the calibration line

One of the most substantial issues of evaluation a gauge calibration is to determine the calibration function. In pursued situation, it means to estimate the parameters of the linear function which express the dependence of the (errorless) measured values using the calibrated gauge on the true measured quantities. Of course, we are interested also in uncertainties of the estimated parameters. In contribution are shown two methods solving the problem. The first one is an approximative method using the linear model of indirect measurements. The second one is a proper approach using the linearized model of direct measurements with nonlinear conditions on the parameters.