take a look at this i believe it will help you
http://www.webwomb.com/basal_body_temp.htm
Your BBT will spike when you are ovulating or after you ovulate, so you may miss your window of opportunity charting that way. The best way to check for ovulation is with an ovulation prediction kit. They are like 20 dollars for 7 tests. It will tell you when you are going to ovulate, the ClearBlue tests will show an LH surge 24-36 hours in advance of ovulation, giving you the most opportune times to BD! Since you only ovulate for 24 hours or less, these are really the best option! Good luck, and SSBD!!