Powered by Standard Media Index's Cross Platform product, the Ad Market Tracker indexes the movement of U.S. advertising investment on a month-to-month basis. Data represented in the index is derived from actual spending by ad agencies representing more than 90% of all U.S. national advertiser investment. Baselined to a value of 100, the index is intended to be a simple way for readers to visualize the supply and demand of ad spending overall, and across the major media.