TV Week reports on Nielsen Co.'s new product that allows advertisers and media buyers to find out whether their spots ran the previous night and how many people saw them. The first client for the product, called KeepingTrac, is media-buying agency Carat. Nielsen said that until now, clients had to wait weeks for reports on when commercials aired. The new product will also allow clients to adjust their campaigns of ratings or demographic targets if they aren't being met. KeepingTrac follows spots on national broadcast networks, national cable networks and local broadcast stations.