Popularization of automatic methods of measuring meteorological elements and substituting manual methods creates a problem of maintaining homogeneity of measurement series. In such situations it is necessary to conduct measurements simultaneously, i.e. using a method being introduced and a former method. The analysis of measurement series carried out simultaneously enables comparing and relating measurements made by a new apparatus to already existing results. The present paper includes the results of the analysis of differences between daily, monthly and seasonal atmospheric precipitation values coming from a 11-year series of simultaneous measurements with a telepluviometer and the Hellmann rain gauge.