Everyone agrees the idea is sound: measuring how TV ads perform, in addition to the shows in which they air. And to that end, Nielsen Research this summer released plans to begin measuring average viewing of commercial pods.

But in the months since, the TV rating service has faced mounting objections from both cable networks and ad buyers that its system is fraught with flaws, and yesterday NBC's group of cable networks, which includes Bravo, USA and Sci Fi, announced that it would not participate in the system.

The NBC cable announcement comes after a number of meetings between Nielsen and cable executives, as well as media buyers and the broadcast networks, and both sides are quick to say they are working toward an amicable resolution on their points of disagreement.

Cable networks applaud the aim of new system. But concerns include the worry that it won't give accurate readings because it relies on one-minute averages taken during ad pods. Others complain the one-minute increments are too long, and there's also concern that they will overlap to include parts of shows in which the ads appear, though Nielsen addressed some of those concerns with a release last week.

Over the summer, Magna Global USA's top researcher, Steve Sternberg, first raised objections to the proposed system, writing in a report: "These are not commercial ratings, nor are they an acceptable surrogate." Sternberg contends that one-second increment are what's needed.

The cable networks have also complained that Nielsen's system doesn't differentiate between national and local ads.

“We support commercial ratings being produced so long as it’s done the right way. The important things that need fixing are how Monitor-Plus reads commercial minutes with respect to cable in its current iteration,” says Sean Cunningham, president and CEO of the Cabletelevision Advertising Bureau. “In its current iteration, Monitor-Plus cannot distinguish between local and national cable commercials, and it cannot capture live sporting events.”

Adds Cunningham. “We’re working hard with our members to go through a lot of fixes. They’ve been cooperative. We’re all participating in fixing it together. It’s not like we’re at odds on anything we have to do.”

Initially, Nielsen had planned to roll out the first round of commercial data in November. That's now been pushed back until December, and even then it will still be in test, not for use in negotiating ad buys. Just when that might happen is still very much up in the air.

“The thing about this is, in the end we’ll probably have a good mix of broadcast and cable networks participating in this evaluation project,” says Nielsen spokesman Gary Holmes. “Obviously every network will have to make its own decision whether to participate or not, whether they decide to opt in now or later or even not at all."

In January, Nielsen will be making additional refinements to the system.

“It’s an ongoing process," says Holmes. "In January, for example, we’re installing hardware on our advertising tracking system – that’s Monitor-Plus – that will allow us to do a better job identifying national and local ads”

But even then a true ad rating system is still a ways off.

"Nielsen is moving in the right direction but what advertisers really want is a true commercial minute rating. That's probably several years away," says Brad Adgate, senior vice president and corporate research director at Horizon Media.

"Advertisers would ideally like to know who watches their commercials," Adgate says. "As DVR penetration increases, there may be more steps needed down the road."