Some insight

Ni

Hoping someone can give me some insight. I couldn’t start using my OvuSense until say 11 due to spotting a little longer than usual.

Got my positive opk on CD 12 along with lots of EWCM. Glow stated I would O on CD 13. My chart states I O’d on CD 16 which is 3 days later than the positive opk.

Can someone familiar with charts give me some insight ?