The percentage of Viewable Impressions as a proportion of Measurable Impressions, calculated using Viewable Impressions divided by Measurable Impressions (Viewable Sales / Measurable Sales) * 100. Viewable Impressions are calculated using the MRC standard. An ad is counted as viewable when at least 50% of the ad shows on screen for one second or longer for display ads and two seconds or longer for video ads.