The resurrected "American Top 40" kept the "Radio and Records" CHR/Pop chart previously used for "Casey's Top 40" and was used as the basis for the show for the majority of this period. The only exception was a brief period from October 2000 to August 2001 when an obscure Mediabase chart was used. This chart had a rather ambiguous recurrent rule, which would see songs removed weekly from the chart from as high as #10, while that chart also resulted in songs that charted/peaked lower than #40 on "Radio & Records" pop charts to appear on the "AT40" charts. By the time Kasem's last show aired, the show had gone back to using Mediabase's charts.