Making Sense of Your Chart
Read this, learn this, live this: you CANNOT make much sense of your chart until the end of your cycle. This is the first thing you need to know about making sense of your chart. This is why it is suggested that you chart for a few cycles (three was my personal standard, but make it more than one) so you can establish a pattern and predict when ovulation will occur.
First, let's take a look at your temperatures. Generally speaking, your BBT is low from the first day of your cycle until the day (or two days, even) after you ovulate. You may have a day or two whose temperatures don't fit; several things could be to blame, like a bad night of sleep, illness, or a night of drinking. As long as a majority of your temperatures in the first half of your cycle are low, things should be fine. After ovulation, your temperature spikes about half a degree and stays high until the day before your next period, when it plummets. Sometimes, the temperature will creep up over several days, sometimes it'll jump overnight. That's why you don't want to read too much into your chart every day as you go along. And just like with the first half of your cycle, you may have an odd day or two where the temperatures don't seem to mesh. Remember, we are looking at the majority of the temperatures being high. (And just like it may take your temperature a few days to reach its peak around ovulation, it may take a few days into your period to go all the way back down again.)
In case you wanted the scientific reasoning behind your post-ovulation temperature spike, it is because of the hormone progesterone. Progesterone is released after you release an egg. Don't release an egg, you won't see the temperature spike. That's why charting is so darn effective!
Next, we will look at your cervical mucus. At the beginning your cycle, you will be recording your flow and even color. (The bright red bleeding usually occurs at the beginning of your period, while it turns brown towards the end. It also tends to start light, turn heavy, then turn light again.) Every woman is different! You may have a light period the whole time, or a heavy period the whole time. Your period may only last 3 days, while another woman's period lasts 7 days.
Usually after your period, you will have a few days of dryness. (If you have shorter cycles, some discharge may be noticed right away.) If you were to wipe prior to using the bathroom, you would notice nothing on the toilet tissue or very slight discharge that is white or cloudy, and almost crumbly. (Note: If your discharge is white and heavy, and is accompanied by an abnormal smell, you may have a yeast infection.)
Over the next week or so (again, depending on the length of you cycle), your discharge will increase, turn more transluscent, and get more slippery and elastic. The more abundant and egg-white your discharge appears, the more fertile you are. This is one of the big signs you are looking for. Now... sometimes your signs will differ from the "normal" cycle chart. Sometimes you may not reach that egg-white mucus, not quite getting there. Sometimes it will continue past your ovulation date. Try to time sex when the cervical mucus is most egg-whitish, before your temperature hits its peak.
Putting these two things together...
Your goal is to pinpoint the day of ovulation. By observing your cervical mucus ain conjunction with your temperatures, you should find the your cervical mucus peaks right before your temperature does. But this is not always the case, and you can still be having healthy cycles that could result in pregnancy without this happening. Sometimes you will continue to see that optimum cervical mucus after your temperature shifts--once your temperature has risen, you are no longer fertile. Sometimes women don't have egg-white discharge. But if you are having temperature spikes and otherwise normal cycles, you know that you are still fertile. Again, I reiterate: you have to look at your overall chart at the end of yor cycle to properly discern patterns. Once you have charted a few cycles, you will be able to really see your body's patterns and can plan accordingly.
What you want to try to establish is how many fertile days you have each cycle--days of good cervical mucus prior to your temperature shift. You want to be having unprotected intercourse on those days, as well as the day OF your thermal shift for good measure. If your temperature takes a few days to climb, there is no harm in continuing to have unprotected sex for those few days as well. Sometimes, a woman releases a second (or third, or fourth...) egg within 24 hours after the first egg is released.
Why Have Sex on These Days? The Life of an Egg and Sperm...
Ovulation = when a woman's body releases an egg. (In case you forgot that point.)
First of all, once an egg is released, it really doesn't live that long, floating around in your uterus. It usually lives 24 hours, maybe up to 48 hours. That's NOT a very big window for conception to occur, which is why you want to make sure you take advantage of it each cycle. Ideally, you want your partner's sperm to be in the uterus, waiting for that newly hatched egg as it travels down the fallopian tube. That's why you want to have intercourse before your temperature spikes; when it spikes, that means the egg is already there and may even be dying. And of course, the more sperm you have waiting for the egg, the more likely you are to conceive. A man's sperm can live up to five days in that "good" discharge that resembles egg-whites. The more sex you have with that egg-white discharge before your temperature spike, the better your chances are of getting pregnant.