For years, Facebook has celebrated — boasted, even — about how quickly video advertisements were taking off on the social network. Then, a month ago, the company found something that has let some of the air out of that balloon: an algorithm it was using to tally up how much video people are actually watching was wrong.

While Facebook said it was measuring the total time people spent watching a video divided by the number who played it, the firm found out that it was actually only logging the people who had viewed a video for three seconds or more. That could have inflated viewing numbers by as much as 60 to 80 percent, according to a Thursday report from the Wall Street Journal. And while Facebook says that it did not affect billing for those advertisers, the Journal reported that some ad buyers are very upset, having based their purchasing decisions on the network's high numbers.

Facebook did not provide more information on how it discovered the error, only disclosing that it happened a month ago. But the mix-up and its repercussions serve to highlight, yet again, just how powerful Facebook has become as an advertising and media firm — and how its own, secret formulas and internal calculations can affect a bevy of other businesses.

In a company statement, Facebook said: "We recently discovered an error in the way we calculate one of our video metrics. This error has been fixed, it did not impact billing, and we have notified our partners both through our product dashboards and via sales and publisher outreach. We also renamed the metric to make it clearer what we measure. This metric is one of many our partners use to assess their video campaigns.”

In the end, video views are just one way businesses make their decisions about advertising. Still, Facebook's vice president of business and marketing partnerships, David Fischer, also apologized to advertisers Friday in a post on the company's website, saying that Facebook immediately fixed the problem and alerted advertisers about it.

"We want our clients to know that this miscalculation has not and will not going forward have an impact on billing or how media mix models value their Facebook video investments," he wrote. "But this isn’t just about this error. This is about how seriously we take our partners’ commitment to our platform, and how their investments with us wholly depend on the transparency with which we communicate."