One of the great challenges of digital advertising is getting assurance that users actually see the ads for which the advertisers are paying. Traditional print media has its problems, but buying page 6 of the September issue of Vogue pretty much guarantees eyeballs.

It’s not the same in digital.

New metrics and standards have cropped up trying to solve this problem. In some circles the idea of the viewable impression has gained steam: measuring an ad’s length of viewability as a proxy for determining the likelihood that it has been seen.

Yet the metric of viewability brings troubles of its own…