Glow and Ovulation Predictions

Hi to all you ladies,
I have been using glow for just short of 12 months, so you'd have thought by now their fertile week predictions would have been spot on. 
Not so. 
I am ovulating a whole week earlier than what Glow has been telling me, had I have not started checking and getting my cycle in check three months ago, I'd still be missing it altogether. 
DO NOT rely on Glow to confirm your ovulation - you MUST either temp alongside this app or take OPK tests.