Illustration 10 e.g. shows em­piri­cally found fre­quency dis­tri­bu­tions of pe­ri­odic du­ra­tion of vari­ous res­pi­ra­tory and cir­cu­la­tory rhythms in sub­jects ly­ing down. Al­though the dis­tri­bu­tions are very wide­spread and show a large in­ter-in­di­vid­ual vari­abil­ity of the rhyth­mic func­tions, the peaks have sim­ple whole num­bered con­nec­tions as sta­tis­ti­cal pref­eren­tial fre­quen­cies and/or fre­quency norms.