CL, you need to chart from CD1 (cycle day 1=1st day of AF) your BBT, MOST IMPT for determining O, Plus note down your CM everyday and OPK helps to identify when you are nearing O. These 3 are the most useful when combined together.
OPK is to show when you are nearing O, in order you BD on time
CM to show stages of your cycle, as in when you are possibly Fertile, Fertile and No more Fertile
BBT charting shows you low temps before O and at the lowest point before you O, after you O, your BBT will move upwards. Then you will know you have O. With BBT, you can only see the chart for O after your temp goes up, so too late by then for BDg, but shows you exactly when you O
So basically you need to combine with use of OPK and CM to to determine when you are NEARING O, in order to BD. Get it?