After a brief review of Westmijze's semi‐infinite model for the reading of recorded signals in magnetic media by gapped ring heads, a program for the computation of the gap loss functionSis described. By introducing the higher order sine and cosine integrals, this function can be evaluated to any degree of accuracy over its useful range. A four decimal place table is compiled and included in this report. Two experiments significant to the validity of the theory and the practical evaluation of the data system performance were carried out with the help of the table compiled. By autocorrelating the system output, the null points in the frequency response curve of tenths of micron (micro‐inch) gaps were located with confidence. The first null point determines the effective gap length accurately, from which the signal amplitude reduction due to gap interference at arbitrary wavelengths can be calculated. Further measurement of output signals at three suitably chosen frequencies enables one to determine the effective thickness of magnetization and head medium separation. The good agreement of the theoretical response curve based on these parameters with the directly measured data indicates the general validity of Westmijze's model. From a practical point of view, the knowledge of these parameters makes it possible to separate the signal amplitude losses during reading operation and suggest proper approaches to the improvement of system resolution.