That one was wrong for 2 of my 3. There are a bunch of other Chinese Gender Charts out there--the one that has been right on for all 3 of mine is:
http://www.parentingweekly.com/pregnancy/pregnancy_information/chinese_calendar.htm
of course, I only found this one AFTER I had 2 kids, and had already conceievd my 3rd, so I didn't get to use it for concieving purposes.