So I'm going to compare two nights. On one night my bbt was around 97.8 (it's usually in that area might be off by .1 sometimes) and then the next night my bbt was 97.08 a pretty big difference I think. The only thing I know that was different was the fact I sleep with the heat on and when I woke up my roommate had the temp set to 60 and I was freezing. So does your air temp play a factor in charting your bbt or should you disregard those days if it's only once in a while that you have that big of a difference? Note: 97.8 is what my bbt is before I ovulate so the decline wasnt after ovulation.