a method for calibration of a path length variable being used for navigating a terrestrial vehicle . the path length variable is measured by determining the number of revolutions of a wheel . for calibration of this value , two speed values are ascertained . a first speed value is determined using the number of revolutions of the wheel and a second speed value is determined using at least one external position sensor . one of the speed values is classified in a plurality of classes , and a calibration value in a class is ascertained using the speed values from this class .