Just adding my 2 cents worth to this discussion....

In relation to Kathryn's question about OPK's measuring O and/or LH, I understand that to an OPK, they are one and the same. The OPK needs to measure a changed in hormones (in this case LH) and that is the "sign" that ovualtion is imminent. The trick is, knowing how far in advance for your body, LH is to ovulation.

In IVF, when your eggs are ready to be picked up, you are given a trigger injection 36 hours before the pick up. This gets the follicles maturing to release the eggs. The doctor will surgically retrieve the eggs as close to the end of the 36 hour window as possible.

But this is 'artificial', and your own natural LH surge may cause ovualtion quicker or slower.

I guess it is a trial and error scenario, with the message being that you have to take all things (CM, OPK, mood, abdomen pains, cycle day, past history etc) into account.

Hayseed