sentences:  "World Tour" continued the series' high sales records with 3.4 million units sold in the United States during 2008.More than 60 million downloadable tracks have been purchased across the series as of February 2010.Both "Guitar Hero III" and "World Tour" were listed on a March 2011 list from the NPD Group of top-grossing games in unadjusted sales in the United States since 1995; "Guitar Hero III" tops the list with total sales of $830.9 million.