How Are The 3 Lunar Months Counted For ʿIddah?

If the woman was divorced on the 1st of the month, then all agree that she will count her 3 months by the sighting of the crescent (hilāl). Therefore, her ʿiddah can be 90, 89, or 88 days.
If she was divorced on any other day, then there is a difference of opinion regarding how to calculate the 3 lunar months: