Grrrr. Accidentally bought the wrong OPK box. Was trying to get the purple kit that tests both hormones so indicates your 4 most fertile days (basically gives you a bit of warning before the window), but bought this very similar looking (and still very expensive) pink set that only tells you on the peak day.
Anyone know if it's the readers or the sticks that do the testing? Ie if I use the new sticks in my old reader, will it give me more information? Probably wishful thinking!