How accurate is glow?

I have been tracking my peroid sense Feb 2014 on glow. And it's great for estimating the days I'm suppose to get my period!! But IV never used it for ovulation before. Is it pretty on track with when you ovulate. And what days you are more lilkely to ovulate then others? If I had sex on the 31,1,2 is there a good possibility I could get pregant. Or is the ovulation app a little off? What's your expectance with it?