Originally Posted by
atomic sagebrush
The rate at which your lines go negative doesn't tell you if you ovulated or not, unfortunately. While the surge and ovulation are linked, they're linked more like your body sending a message to itself to do something, and then it does the thing on its own timeline. The OPK measures ONLY the surge (the message) and NOT the ovulation (the thing it's doing).
So it's possible to have a positive for days after ovulation if your body takes a while to clear out the hormones, and it's equally possible to have your test have gone negative before you've even ovulated, because your body got the message and cleared out the hormone even though it hadn't completed the task yet.
That's all very confusing, so to put it in concrete terms, it's like your boss wants you to call Cleveland, so they put a Post It note on your door to that effect. Maybe you take the note down and call immediately. But maybe you call immediately and leave the note up for a few days because you forget to take it down. Maybe you take the note down and don't call for a few days. Maybe the note falls off and you forget to call (the test goes back to negative again, but ovulation still hasn't occurred.) Maybe you leave the note up and forget to call totally (this is what happens when people get days of positive OPK and ovulation never happens.)
The message and the act of ovulation are two separate events and the OPK only measures the message!