The “in-line” and “on-line” linearity terms of a linear calibration are defined. “On-line” linearity, which is calculated from the standard deviation of the slope, is proposed as a performance characteristic for the analytical method. The relation between the precision of an analytical result, and the analytical sensitivity and “on-line” linearity of the corresponding chemical calibration is established. The simplified equation that is obtained makes it possible to rapidly estimate the standard deviation with a sufficient degree of freedom, even when few analysis replicates are available. An indication is also given of the suitable equation for a more accurate calculation. The use of the two linearities, both “in-line” and “on-line”, is discussed, concerning the determination of the linear calibration range, for those techniques with which curvatures are obtained when the concentration of the standard analyte exceeds a particular value.