Noninvasive systolic and diastolic blood pressures (P_syst and P_diast, respectively) are often measured by applying the fixed-ratio oscillometric method, which determines blood pressures using empirically estimated fractions of the oscillometric amplitude envelope. These fractions are known as characteristic ratios (k_syst and k_diast, respectively). A review of studies over a more than 20-years time course shows a noticeable variation of characteristic ratios estimated by different researchers. We compared the literature-based data with data obtained by modeling of the fixed-ratio oscillometric measurement. The results suggest that if the between-study variation of characteristic ratios is described as a change in the difference k_diast - k_syst, then the observed variation can be explained by differences in the symmetry of the arterial wall pressure/volume relationship of the studied groups, and also by differences in cuff handling. In contrast, if a parallel shift of k_diast and k_syst up or down exists, this refers to the different pulse pressure and/or different steepness of the pressure/volume relationship of the studied groups.