So, depending on the legal framework, a 28 day marker could be very useful. If they were actually tracking the moon, you’d think it would be 29 units even though a lunar month can vary between about 29.1 and 29.9 days. Then again, 28 notches on a stick means 29 sections, so…?
It’s interesting that a woman’s menstrual cycles is approx 28.1 days on average, with a standard deviation of 3.95 days. That means 28 days is a lot closer to the average menstrual cycle than the average lunar month. But, the standard deviation is a lot greater.