Quote Originally Posted by pinkdusty View Post
Atomic.. please do let me know if the difference is only the duration. I will like to subscribe soon. Also, what is OPK?
No the one has additional e-books that come with it. It's the number of books.

OPK are "ovulation predictor kits" that detect hormones in your urine that happen before ovulation. It helps us know when to have intercourse to conceive.