Basal Body Temping (BBT) charting is a great way to pinpoint exactly when you ovulate. I first want to say that this is not the best idea for beginners. It can take a bit of dedication, and in my opinion can create stress. If you are in the first months of trying-to-conceive.... enjoy it. Try ovulation prediction tests first. I started charting a couple months ago. After 7 cycles with no success, and trying to just use ovulation prediction tests, I felt it was time to try BBT charting. First, you need a special thermometer. You need to purchase a basal body thermometer. This is the thermometer I purchased at Wal-Mart. It works wonderfully.... saving your highest temp, and your previous temp, which can be important if you forget to enter your temps into fertility friend right away. http://www.walmart.com/ip/Reli-On-60-Second-Basal-Thermometer/10161099
Now you could use a normal, oral thermometer, but it not recommended. The BBT thermometer is so much more accurate. To start charting you will need a fertility friend account. This is what I use for charting, and I love it. They even offer VIP membership for free at first (which afterward you can still use the free version, which still works great). Here is the website for fertility friend. http://www.fertilityfriend.com/ttc/login.php
After you have this in place you can start charting. It is best to start charting on Cycle Day (CD) 1. This is the first day of actual menstrual flow (not spotting). Take your temperature when you wake up, before rising. Also try to take your temperature at the same time every day. If you cannot take your temp at the same time, you need to adjust the temperatures. If you wake up an hour later subtract .2. If you wake up an hour earlier add .2. Also make sure you have slept at least four hours before taking your temp. I recommend "practicing" before CD1. I stated temping a week before CD1 to get practice. Next, let's go into more detail pertaining to BBT charting. In the beginning of your cycle estrogen is dominant. This causes lower temperatures. A day after ovulation a spike in temperature will occur, and then temps will stay up. This is because progesterone is dominant. This pretty much creates two different levels of temperatures. The lower pre-ovulation temps, and the higher post-ovulation temps. Fertility friend does all the work for you. All you have to do is put the temperatures in. Fertility friend will do the rest, marking ovulation and drawing up a coverline. Fertility friend will mark ovulation after three days of higher temps that are above the coverline. This is why using ovulation prediction tests is important. You will not know that you ovulated until after you ovulated. Ovulation prediction tests will give you an idea of when you are going to ovulate. The temperature shift informs you that you did ovulate, then three days later fertility friend will mark the day of ovulation three days prior. Here is my chart from last month. Notice the two different levels, and where ovulation was marked. You can also see a red dotted coverline.