I use one step ovulation tests (cheapest I can find them is ebay). Mine was completely negative one day, and then a definite solid positive line the next. I have clear blue digital ones with a blank circle for no and a smiley face for yes so it takes some of the guess work out of it. I use these when I think I have a positive on the cheap ones, just to double check. Using digital ones every day can work out expensive, so most people use internet cheapies- especially if you're going to be testing every day x