Viewability is an optional statistic that can be tracked by AdButler. An ad which is “Viewable” is one which was measured to be within a user’s visible window (not scrolled off screen) for at least one full second. You can read more about viewability here.
Any time an ad is sent to a publisher, an impression is recorded.
Once an ad is received by the publisher’s page or app and is inserted into the HTML document, it becomes “Eligible” for viewability. That is, it will be actively measured to determine if the ad is on screen.
An ad is “Viewable” when it has been in the visible portion of the a user’s screen for at least 1 continuous second.