- The number of days is different in each calendar month.
- The week and month cannot be aligned. The number of weekends is different in each calendar month.
- The number of working days is different in each calendar month. It ends up that the number of days in each quarter is also different.
- The period closing day will fall into different days in each period. The accounting department prefers always close the period by a given day in a week, such as Wednesday or Friday.
