Ive been using this app for over two years now and its great. It helps me track my cycle really well unless of course I forget to put it on the calendar. However, its really helpful because it may be one or two days off of when I may start again, but it helps me sort of look at the big picture. And see when Im ovulating and when I may be getting my next period, so it helps me prepare.
Hiehiheisj about Period Tracking Calendar, v9.6