It was a was a throwaway line on the 50th slide in a PowerPoint deck. But that seemingly innocuous bullet point -- "Time as a currency to trade?" -- stands to upend the digital-advertising industry.

In March 2013, Jon Slade, commercial director of digital advertising and insight at the Financial Times, presented the idea to the paper's Asia sales staff. Next month, the London-based paper will roll out ad rates based on time rather than impressions, charging some advertisers by the number of hours their ads appear in front of targeted groups of readers. The measurement -- cost per hour, or CPH -- shatters a decades-old media pricing model that values volume above all else.

"We're definitely challenging the status quo," Mr. Slade said. "No one has come up with a new currency in digital advertising in -- a while."

The internet is awash in page views. In August, roughly 3.5 trillion web pages were loaded on computers worldwide, according to measurement firm ComScore. Ad dollars are going with the flow, with internet advertising revenues in the U.S. reaching $43 billion last year. But about 70% of that went to the top 10 ad-selling companies, including Google, Yahoo and Facebook. Large ad networks siphon off much of the rest, leaving premium publishers parched. Those publishers have also been hurt by the shift to mobile, where rates are significantly less, as well as downward pricing pressure from increasingly automated ad sales.

This moment matters for publishers like the FT, according to Jason Kint, CEO of Digital Content Next, formerly the Online Publishers Association. "We're in a medium that's fast changing and evolving," he said. "I'm hoping we'll look back a decade from now and see this as a critical milestone."

Such a radical rethinking of ad rates would have implications far beyond publishing. Assured that people are spending time with their messages, marketers would give budgets a fresh look. The foundation of the analytics industry would shift. Creatives would need to take digital-display ads more seriously. And media agencies would have to adjust how they buy ads.

"It'll be more like TV, with metrics that [advertisers] understand and can relate to," said Shenan Reed, president of digital at the media-buying agency MEC North America.

Creating scarcity
More than half the FT's revenue comes from subscriptions, two-thirds of which are digital. (Its publicly traded parent company, Pearson, doesn't break out revenue for the paper.) It has about 677,000 subscribers, but its web and mobile websites attract a relatively small audience. During the second quarter, the FT averaged about 12 million monthly unique visitors across desktop and mobile, the paper said.

To compete with publishers that have larger audiences, the Financial Times has leaned on data it collects firsthand to do a better job slicing up its audience for advertisers. And while its audience may be smaller, it is mighty in terms of affluence and the time readers spend on the site. That's why, in the battle for ad dollars, the FT is at the bleeding edge of the movement toward so-called attention metrics.

Other publishers have joined the cause. The Economist, which is part-owned by Pearson, is guaranteeing time for its in-app ads. While it doesn't currently charge advertisers based on attention, Upworthy measures "attention minutes." Gawker is holding internal discussions about ways to make ad viewability and attention a new standard, according to one person involved in those meetings. The Wall Street Journal is using attention metrics to analyze and adjust ad campaigns. And a slew of other publishers are working to ensure their ads meet a viewability standard established earlier this year.

Putting the focus on time rather than views is an attempt to create scarcity, the concept that allows media companies -- particularly TV networks -- to slap hefty price tags on commercial time. There are only so many 30-second slots during a half-hour sitcom.

"Time is the only unit of scarcity on the web," said Tony Haile, CEO of Chartbeat, a digital analytics company that was recently accredited to measure ad viewability by the Media Ratings Council, a standards organization.

"You've only got 24 hours a day per person. So what you've got is a constrained resource: time," he said. "That directly correlates with the goals of advertising. Just like any economy of scarcity, anyone who captures most of it can charge more."

Emphasizing time doesn't necessarily reward long-form content at the expense of quick hits, but it does value giving people what they want. Publishers can still win the attention metrics game with cat pictures as long as they're really good cat pictures. It doesn't require publishers to invest in deeply reported stories displayed in HTML5 layouts. Upworthy, for instance, keeps people on its site with videos mined mostly from YouTube. The trick is finding the right videos.

Publishers aren't the only interested parties. Some media buyers are also pushing for attention metrics. "It's right for the client and where the industry will ultimately be heading," said Ms. Reed, who advocates for a cost-per-30-seconds standard for time spent with an ad. "I've been wanting to get to us buying like this for some time," she said. "It's one of the most valuable metrics in the business."

Tom Penich, media communications manager at BMW of North America, said he's "very interested" in an attention-metrics model. "That's an area that we see as more of a brand tactic so there are more interesting things to do and something where we become much more interested in the time spent," he said.

Entrenched interests
But there's also plenty of resistance. Spending on digital-display ads in the U.S. was $13 billion last year, making up 30% of the $43 billion earmarked for digital advertising, according to the 2013 IAB/
PricewaterhouseCoopers Internet Ad Revenue Report. Display was second only to search advertising, which declined last year, the study said. With so much money sloshing around, there are a number of players that would prefer to keep the current order.

"Agencies are among the entrenched interests," said Benjamin Zeidler, director-research and analytics at digital-marketing agency Tenthwave. "They're good at buying ads. They know how to do it. It's probably scary to change the mode of how they do business -- how they sell it, price and benchmark it."

Publishers that attract huge audiences aren't eager to see a shift either, said Paul Rossi, president of The Economist Group. "There are a lot of people for whom the current system works quite well."

Neither the Interactive Advertising Bureau nor MRC has tackled the subject officially. "IAB has not gone to MRC with the notion that attention measurement merits a task force and needs to be standardized," said Sherrill Mane, senior VP-research, analytics and measurement at the IAB. "We may or may not go down that path."

There's also the question of whether more time on a screen would do an advertiser any good. Readers are more or less trained to ignore banner advertising, a phenomenon called "banner blindness." A 2013 study by Infolinks, which helps publishers and brands make their ads more noticeable, found that only 14% of respondents recalled the last display ad they saw and the company or product it promoted.

"Whether they're looking at the ad or the content, we don't know that," Mr. Slade said.

'That's a success'
For the last 20 years, most digital advertising has been sold on a cost-per-thousand impressions, otherwise known as CPM, squarely rewarding the volume of visits. The more eyeballs a site delivers, the more it can charge advertisers. Publishers also bolster their CPMs based on viewer demographics and sometimes by using additional metrics, including the amount of time spent on a page. Some media companies began offering time as a secondary guarantee to digital advertisers almost 10 years ago, according to one former TV executive. Other sites have looked to social media to strengthen CPMs. BuzzFeed, for example, supplies advertisers with "social lift," a proprietary metric that measures how many people see a post because of sharing on social media.

Still, reader engagement is often based on whether a person actually clicks on an ad -- the so-called click-through rate, or CTR. At roughly 0.1%, the CTR for display ads is laughably low. Yet the click-through continues to show up on media agency reports, despite efforts from publishers and media buyers to kill the measure.

Moving marketers away from outdated metrics has been a slog. Romy Newman, head of digital advertising at The Wall Street Journal, recalled an ad campaign the Journal ran 18 months ago for an enterprise- technology company that targeted chief technology officers. "It's probably an audience that doesn't have a high propensity to click" on banner ads, she said.

The advertiser measured click-through rates and canceled the campaign after two weeks citing lack of performance. But the Journal reviewed attention metrics and found a different story. "We told them their ad was in view to their CTO target for an average of 56 seconds -- that's not a failure, that's a success," she said. "Where else will you get that much time from the CTO?"

Massive transition
Attention metrics come amid a broader industry discussion around display-ad viewability. In March, MRC issued a set of rules around viewability in collaboration with the IAB that said an ad is considered viewable when at least 50% of it shows up in the viewable portion of a browser for at least one second. In theory, ad rates should increase because there are fewer viewable ads. However, several publishers said their ad rates were still facing downward pressure and many had incurred additional costs shaping up their web pages to ensure their ads are within view.

"We're still in massive transition mode and there's lots of complaining and concern," said Mr. Kint of Digital Content Next, which represents over 50 publishers, including The New York Times, ESPN and Vox. "The transition phase will be hell for everyone."

Mr. Slade said that he believes the IAB standard wasn't strict enough, but that it was the first step toward solving a lingering problem: Nearly half of online display ads are never seen, according to ComScore. It was against this backdrop that the Financial Times started looking at the viewability of its ads and, eventually, attention metrics.

"We found there are a whole bunch of impressions that are on screen for more than one second, and two and five and 10 seconds," Mr. Slade said. "And actually we're not valuing those correctly and nor are the agencies that buy our media."

Using technology from Chartbeat, the Financial Times starts its timer when at least 50% of an ad has appeared on screen for five seconds. "Any time an ad is on screen for five seconds or more it goes into a pot of one hour," Mr. Slade said. If a reader scrolls or clicks away from the ad before five seconds have passed, the time doesn't count toward the hour of time an advertiser has bought.

To determine whether a reader is active on the page, Chartbeat looks for signals, such as mouse movement and keyboard activity.

According to a Financial Times analysis, readers who saw an ad for at least five seconds experienced, on average, 79% greater brand recall. In addition, across the study, it saw an average uplift across brand measures like familiarity, association and consideration of 62% when readers were exposed to an ad for that long, Mr. Slade added.

He declined to say how much the Financial Times would charge for an hour of time, but he said it determines cost per hour by looking at CPMs, effectively backing into a number.

"When you buy a thousand impressions on any website, you are inadvertently buying time as it is -- 20,000 impressions creates a period of time as they're served out," Mr. Slade said.

"We're not trying to gain any price advantage on this, so we're equating the cost per hour to roughly what you're already buying as a CPM," Mr. Slade said. However, in a follow-up conversation, he conceded that the company will "think about how we evolve our pricing model." The Financial Times is looking for six advertisers during the next three months to buy on a cost-per-hour basis. Other advertisers can continue to buy impressions based on CPM.

Getting creative
A shift to attention metrics would not only change how ads are bought, but how they're made.

"If this were to become standard -- and I'm not saying it is -- it would certainly shine a spotlight on the quality of the creative and put more accountability on agencies and marketers to make sure the creative is more compelling and appealing and elicits greater connections with consumers," said Ms. Mane.

Andrew Essex, vice chairman of creative agency Droga5, said creatives want to do work that's qualitatively superior. "They don't want to produce stuff that's pollution," he said, referring to poorly done banner ads cluttering web pages.

However, a new way of valuing banner ads might inspire them to reconsider the medium, according to Mr. Essex. "They would be dealing with more complicated audience responses that I think are more human than simply the number of people attached," he said.

With the viewability standard in place, creative agencies should expect the ground to continue shifting toward attention metrics -- whether cost per hour, cost per 30 seconds or something else. "I don't think it will be one single metric," said Jonah Goodhart, CEO of Moat, a digital ad analytics firm. "We will see a shift on transacting on viewability in late 2014 or early 2015," he added. "This idea of buying media on the metric that makes the most sense for you is where we'll see the world going."

Ms. Reed was even more assertive: "One year from now it becomes a common way to buy, and eventually it will become the way to buy."