speaking from my own experience, I think the best way to find out our ovulation date is by taking daily basal body temperature and by observing our cervical fluid everyday.
I strongly recommend all women read the book called "Taking Charge of Your Fertility" by Toni Weschler, MPH. You can learn more about your cycle and better pinpoint the day when to have sex when you want to get pregnant or when not to have sex if you want to use it as a birth control method. Very useful...
I think you should be able to find it in any big bookstore which carries english books. Try the one in Time Square (Page One) or the one in Festival Walk, I believe they should have it.