The Subscription Fee is subject to a annual indexation by Supplier in accordance with the US Consumer Price Index (CPI) plus three percentage points. The index number for the month of September shall be used for the subsequent calendar year. Any index-related increase in the Subscription Fee in accordance with the paragraph shall utilize the monthe of September of the year 2010 as the base for calculationn purposes. Supplier will upon a written request provide Customer with documentary evidence of any index increase. If the index is negative for any particular year, the prices shall remain the same and shall not be adjusted downwards. If Customer so requests, Supplier will provide Customer with documentary evidence of any index increase.