Dive Brief: 

• The Media Rating Council introduced its interim guidelines for what consists of a "viewable" ad on mobile—a move meant to hold the industry over until the MRC and ad-industry group Making Measurement Make Sense develop more lasting standards. 
• The guidelines mimic last year's desktop standards that count an ad as "viewed" when at least half of it is within view for at least one second; videos must be viewed for two seconds. 
• The MRC also introduced a new mobile category called a "loaded ad," which is an ad that falls between a viewable impression and not appearing on screen. Loaded ads must have 25% of the pixels in view for one second. 

Dive Insight: 

Defining viewability on mobile will be a huge project to tackle. Similar to desktop practices, many in the industry will disagree on what constitutes an impression. And with varying mobile screen sizes, the measurements are more complicated.