Radio altimeters are based on the principle of radio location of the earth’ssurface using a frequency-modulated standing wave. The relatively simple method ofmeasurement consists in the evaluation of the number of pulses generated as resulting fromthe mixing of the transmitted and received signals. Such a change in the number ofmodulated pulses within a certain altitude interval, however, is not so simple and is adeterminant issue in defining the precision of the radio altimeter. Being knowledgeable ofthis law in a wider context enables us to enter into discussion on the possibilities of furtherincreasing the precision of measuring low altitudes. The article deals with the lawunderlying the change in the number of radio altimeter pulses with the changing altitudemeasured.