The previous dates that are utilized for comparison should reflect the historical window that is most similar to the current situation. This could be four (4) years ago for say Olympics programming sales, or perhaps as recently as last quarter for a new series that has little history. The only limitation should be that the final bookings are invoiced for this comparison period (by that we mean that the period has passed). Another key element of the comparison is that the previous period being compared must have the same number of days of business. This for the most part precludes a Broadcast Calendar and implies a Fiscal Reporting calendar for most situations. Another consideration for a valid comparison is that the previous comparison date should fall on the same day of the week as the current day (again supported by a Fiscal Calendar).