PeanutButter, I think you might be right. I bought mine on Amazon cheaply (50 at a time). Which ones do you use?
Belle, my tests say that as dark as the control line or almost as dark is the LH surge, ie positive ovulation test. I've also just remembered that my doctor said that if you get the luteal phase temperature rise (if you are tracking temperature) and regular periods then you are ovulating. When you don't ovulate your periods go weird or very light. So now I'm watching the thermometer closely but it hasn't gone up yet.