When creating corporate reports, you often have to update last quarter's dates from, say, 7/31/2006, 8/31/2006, and 9/30/2006 to this quarter's, and it's error-prone because the number of days in each month must change as you do so. (e.g. 8/31 must change not to 11/31 but to 11/30.)
Instead, I suggest:
Jan = 30 days Feb = 28 days Mar = 31 days
Apr = 30 days May = 31 days Jun = 31 days
Jul = 30 days Aug = 31 days Sep = 31 days
Oct = 30 days Nov = 31 days Dec = 31 days
Now when you have a report with dates labeled 7/30/2006, 8/31/2006, and 9/31/2006 and you need to increment the months, you don't have to change the days because the days are periodic.
(Except for February which continues to operate as before.)-- phundug, Jan 14 2007random, halfbakery