OPKs don’t tell you when you ovulate, they show when conditions are favorable. Monitoring BBT can confirm ovulation. Also... why save dried out tests when you can log them when fresh in any number of apps?! (I recommend PreMom)

OPK's don't tell you when you ovulated, they indicate an LH surge prior to ovulation. If you continue to use OPK's even after a positive result, the next negative result you get will indicate you've ovulated as the LH surge is now over.