A system for calibrating vector corrected electrical measurements to adjust for distortion due to reactance in the measuring circuit, particularly that caused by variable positioning of a circuit element, such as probe or coupling. Initial error factors for directivity, source match, and frequency response, respectively, normally calculated from assumed reflection coefficients of respective primary impedance standards, are adjusted to correct for such reactance. Reflection coefficient measurements (magnitude and phase) of a further impedance standard, different from the primary standards, are obtained at multiple frequencies and corrected by the initial error factors. The corrected magnitude and phase measurements of the further impedance standard are compared with theoretical magnitude and phase values which very linearly with frequency, and the initial error factors are adjusted so as to minimize any deviation of the corrected measurements from the linear values. Thereafter, by positioning the probe or other circuit element relative to a device under test substantially identically to its previous placement relative to the further impedance standard, the adjusted error factors can be used to obtain corrected measurements with minimized magnitude and phase errors due to reactance.