Just a note on OPKs. It works on the idea that the 'average' woman will have a surge of LH. So basically control line is set at the minimum surge level for the 'average' woman, and looking for the line equal to or darker than the control is just basically looking to see if you have more than the minimum amount of LH that the average woman surges on, and would cause ovulation. If you aren't the average woman, OPKs aren't truly accurate, as sometimes you will never get a true positive. Alternatively, if you aren't that average woman at the other end of the scale, and you don't ovulate unless you have a higher than average LH surge, getting a positive result might not necessarily mean anything except that you have a higher than average amount of LH in your urine.

Hope this makes sense