When working on the Estimating tab, you can switch between two modes of operation: Trending and Estimating.
Trending Mode
Trending mode is the default configuration and displays 8 drop down lists that allow you to select from one to eight Actual Books to be used in retrieving historical statistics.
Estimating Mode
Estimating mode allows you to switch to a research configuration and to select one or more estimate books to be used in retrieving estimated statistics.
When you are working with a television buy and switch to Estimating mode, you will be able to use data from Share and PVT books to calculate ratings.