|Coverline is a term used in BBT charting.
A line drawn on a fertility graph that represents a
measurable shift in the ovulatory cycle from the follicular phase to the luteal phase
(with ovulation occurring in between.) Once 6 days of temperatures have been noted on a graph,
the first BBT that is charted at .2 (two-tenths) degree higher is considered a 'thermal shift'.
The coverline is then drawn one-tenth degree over the previous six temps.
If following temps are above the coverline for at least three days, ovulation is assumed
to have taken place.