The migration of users accessing online content mostly from a computer screen to a mobile device is turning everything "on its head," former Yahoo CEO Carol Bartz told CNBC on Friday.
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"This whole change to a different screen is just taking every metric and turning it on its head," she said. "Mostly revenue, which is the worst metric of all to have a problem with."
Since Bartz's tenure at the helm from 2009-2011, new Chief Executive Marissa Mayer is the third CEO to try to engineer a turnaround of the company.
Mayer left Google and joined Yahoo last July, but she's already taking advantage of her relationship with her former employer. On Wednesday, Yahoo entered into a non-exclusive arrangement, under which it'll begin to draw on Google's big online advertising network to display ads against Yahoo content.
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Yahoo stock has risen nearly 30 percent since Mayer took over. But it would still have to more than double from current levels to reach the all-time highs of about $48 a share back in 2000.
"I'm still a shareholder. I love Yahoo. I love the people. I love the brand. I love the products," Bartz said. "Yahoo is going to be around for a long time. And Marissa and the gang … are working hard to make sure that's going to happen."
During the company's latest earnings call, Mayer pointed to the recent overhauls of Yahoo Mail and their photo site Flickr, and said it is working on a dozen new products aimed at a variety of "digital daily habit[s]."
In her first full quarter as CEO, Mayer reported fourth-quarter earnings that beat expectations, but guidance for first-quarter revenue was a bit lower than analysts' estimates.
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While Mayer has been concentrating on products, Bartz said that when she had been CEO her team focused on Yahoo's backend: "We worked hard on the behind the scenes. We had to get the engine going before we could get the beautiful outside and the dash, all those things, to use a car metaphor."
Addressing concern about Yahoo not having traction, Bartz countered, "It's still serving 800 million people. So to say it doesn't have traction — when we get all excited about some site that has a million new users — it's like, really?"
—By CNBC's Matthew J. Belvedere; Follow him on Twitter @Matt_SquawkCNBC