Google rolled out a major change to AdWords this week by introducing CPM bidding by viewable impressions. This change was first noticed by Kim Clinkunbroomer of Philly Marketing Labs.
Rather than charging advertisers on the traditional model of served impressions, this change to CPM bidding means that advertisers will be charged based on ad impressions that can actually be viewed in-screen by users. All campaigns running on the Google Display Network will now have this option.
Read more: http://www.searchenginejournal.com/google-introduces-change-adwords-pay-viewable-impression-cpm-bidding/79547/