Escalation Procedure Tentative Rates for those species and products listed in A4a are subject to quarterly escalation in accordance with the following pro- cedures: The calendar quarter index average for each price index described in A5 is the arithmetic average of the three such monthly price indices preceding January 1, April 1, July 1, and October 1. The difference between calendar quarter index average and Base Index listed in A4a shall be the basis for quarterly escalation. To arrive at Current Contract Rates for timber Scaled during the preceding calendar quarter, Tentative Rates for each species shall be reduced or increased by such difference, except when the calendar quarter index average is: (a) Less than the Base Index, the reduction shall not result in a rate below Base Rate or (b) Greater than the Base Index, the increase shall not exceed the difference between Tentative Rate and Base Rate. In the event of Contract Term Extension, the escala- tion procedure will be used during the extension period, except that adjusted payment rates for any calendar quar- ter cannot be less than Tentative Rates, for each species and product group, established under B8.23 for the ex- tension period.