Drawing a coverline on your bbt chart is not required but it will help you to see if you have a biphasic chart (two phases). Most people use the Fertility Awareness method because it is the easiest way to draw a coverline. Once you draw your coverline you should be able to see a pattern of lower temps before ovulation and higher temps after ovulation.
Fertility Awareness Method for Drawing Your Coverline
Make a note of the highest temperature in this six day time frame. You will want to start looking for a temperature that is at least .2 degrees (Fahrenheit) higher than the highest temperature during these six days.
Once you see this temperature rise, you will want to draw your coverline.
If you have an abnormally high temperature follow the rule of thumb on high temperatures and disregard this temperature when drawing your coverline.
Find the highest temperature in the six days prior to the temperature shift and draw your coverline 1/10th of a degree higher than the highest temp in the six day block.
Once you draw your coverline, you can use it to evaluate your chart. Your coverline will probably be different during each menstrual cycle.