The coverline is more used to visualize your thermal shift. Some women have temps that drop below coverline when AF is coming, some women's temps stay above coverline until AF is gone.
Jan15 December Siggy Challenge: Holiday Fails
TTC Since 4/13 | Me: 28 DH: 29 | DX: PCOS + High T + Arcuate Uterus (11/13)
According to TCOYF a coverline is determined by noting the highest of your 6 temps before your temp rise. The coverline is one-tenth of a degree above the highest of those 6 clustered temps.
To my knowledge, it's not used for anything special. As stated before, for some people when temps drop below it they know AF is coming...but temps can drop below and AF doesn't come. It would depend person to person I guess.
Jan15 December Siggy Challenge: Holiday Fails
TTC Since 4/13 | Me: 28 DH: 29 | DX: PCOS + High T + Arcuate Uterus (11/13)
Re: What is a cover line?