Abstract: The transfer of the temperature of a body to a fertility calculator (7) is only authorized by the time controller (20, 23) when a first counter shows that a first preselected period of time (e.g., 22 hours) has elapsed since the previous temperature measure and when a second counter (23) shows that the temperature is being taken during a second preselected time interval (e.g. 4 hours) following the first period of time. Accordingly, only one measure can be made per day at approximately the same time, thereby eliminating the important problem encountered when the temperature is taken at irregular intervals.