NEW YORK (AP) -- Starting next fall, Nielsen will begin counting television programs watched on mobile phones and tablets within its traditional TV ratings.

The company responsible for measuring TV viewership said Monday it will use codes embedded by networks within the programs to collect this information.

Nielsen's measurements are the lifeblood of television's economic system, and this development is an important step in adjusting to changes in how content is consumed. It is not expected to have an immediate, dramatic impact in the ratings since Nielsen estimated that only 6% of current viewing is not measured now. But the impact could be bigger on programs that appeal to young people who are more apt to watch on mobile devices. Nielsen's ratings are used to set advertising rates.

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