To add to that, I actually know a friend of mine who has tried for a girl for 10 years. She has 5 children. All boys. She tried everything, even the sperm seperation. No luck.
There really is no set way to get the gender you want. Even having scientists seperate sperm that they think will be male or female doesn't 100% give you a boy or a girl.
Conception calendars are fun to look at and it's neat when it's a coincidence...but it's just that. A coincidence.