Getting rid of paper diaries after 60 years isn’t easy for Nielsen.

Nielsen is telling its clients there will be a short delay in getting new local ratings in mid-size and smaller markets. And it says that competitors using big data to measure local viewing should take another look at their numbers because converting set-top box data to accurate viewership numbers can be challenging.

In 2016, Nielsen announced that it will replace the paper diaries that Nielsen families use to record what they’re watching on television by collecting data electronically from meters and set-top boxes. The original plan was for diaries to be history by 2017.

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