Glow predicts ovulation day?

Allison
All of a sudden my Glow BBT chart shows that yesterday I Ovulated. It actually says 'ovulated' on the graph.  I've never seen that before. I'm tracking my BBT and using Ovulation kits, but my temp hasn't spiked yet, just stayed the same.  Anyone else have this?  How does it determine the day you ovulated?