This is an additional information for all girls….. check out girls, something i read online

calculate to know which are the fertile days for you, take the reading and note down your menstrual cycle for 5 months, The starting day (1st). then compare the days between your last day and the first day of next month for the 5 months. Take the least number and minus it with 18, take it as A. now take the largest number and minus it with 11, take it as B. now your fertile day will be from A to B. cool ha.

Eg :
5 readings = 27 , 28, 30, 31, 27

27 -18=9

so your fertile days are from the 9th to the 20th of the month.