Simple day counter for reproducing theoretical calculations. This day counter tries to ensure that whole-month distances are returned as a simple fraction, i.e., 1 year = 1.0, 6 months = 0.5, 3 months = 0.25 and so forth. this day counter should be used together with NullCalendar, which ensures that dates at whole-month distances share the same day of month. It is not guaranteed to work with any other calendar.