Useless

Cant figure out how this works. I work in app development so I can figure most apps. I want to enter the first day of my cycle, length of period, number of days in my cycle and get the calculations done. Save the infor till next period.
The free apps i tried do just that. This app doesnt.

Char23-768 about Fertility Clock: menstrual period + ovulation log, v2.3