I started using it recently, so it only has 2 periods in it, and from those dates it's guessed my third period would have been... 2 days ago. 
Should I wait and see? It's only had two other periods adding into it like I say so I guess it's still estimating for now really. I've not added temperatures, just menstruation and discharge (eg eg white mucus).
I'm not going to make my mind up either way, am going to wait and see a couple more days before I think of testing, but I just wondered what other's experiences were?