The following graphic illustrates the individual processes of the female monthly cycle and shows how they are reflected in the temperature curve.
The menstrual cycle varies individually from woman to woman. An average
cycle is assumed to be 28 days. Some women may have shorter (26 days) or
(33 days) cycles.
Generally, a woman will eventually have a
regular cycle and the computer will use this personal, stable cycle as a
basis for its calculations. After some time, if the user has regularly
entered her monthly information, the computer will know that this
particular woman as you can see in this example:
will always ovulate on the 15th day of the cycle and her monthly period will start after 29 days. This is because ovulation causes a slight, but easily detectable increase in the body temperature. Likewise, the temperature will drop back to normal when menstruation starts (defined as the beginning of a monthly cycle). This is the pattern on which the computer bases its calculations to specifically filter out the six days of a cycle when conception could occur.