The clearblue digital detected the LH surge which occurs 24-48 hours before you ovulate. I think the OPK was correct and you had the most CM when you ovulated after your LH surge. The OPKs work because they let you know in advance that your ovulating soon. If you got a positive OPK and ovulated the same day most people would miss thier chance to get pregnant. I read the lines from the tests that come from the digital sticks once you take them out are not accurate and you should go by what it shows on the screen.