Answer: You should begin using the Lady-Comp fertility computer as soon as you receive it. As documented by the manufacturer's FAQ, "The green-light (Infertile) display is just as reliable on the first day of use as it is after two to three months of use. The difference is that at when you begin using the Lady-Comp the green light will appear less frequently.

You can begin to use LadyComp on any day of your cycle. The first menstruation after stopping the pill is a result of the withdrawal of the pill. It would not be necessary to input data regarding this menstruation, as it was not natural. The next menstruation that occurs while not taking the pill would be entered as relevant data. Until you have had your first natural menstruation, you will receive more yellow lights (learning days are always considered as Fertile) and red-light (Fertile) days. Once the computer has detected an ovulation and a natural menstruation you will receive an increasing number of green-light (Infertile) days. With regular cycles and compliant use LadyComp takes approximately 3 months to narrow down the fertile days to the minimum for your personal cycle. Most women receive at least 8-10 red-light (Fertile) days per month.