We've got a bit of TV 101 today, thanks to some new ratings info from the Nielsen Co., those friendly folks who wire a handful of homes and determine what shows live and die.

Nielsen is evolving and has started measuring viewership of ads -- which, obviously, is what advertisers pay for -- instead of just getting ratings for the whole package of programming, ads, promos, etc.

The findings are complicated and incomplete, but they are also intriguing. First, however, some quick background.

In this era of whiz-bang devices such as DVRs (digital video recorders, which include TiVo), there's been a growing fight between the networks and the advertisers over how to figure ad rates.

It starts with the question of how many viewers skip ads when they record a show to watch later, but there's a second battle, too. With postponed viewing, there is a legitimate debate over how valuable delayed ads might be, even if they are watched.

For instance, spots scheduled for Thursday nights can involve weekend movie openings or car sales. If those ads are seen the following Monday, they're worth much less. On the other hand, ads for soda or insurance have pretty much the same value whenever they are watched, unless one of them gets turned into a sitcom about cave men. But we're not going there.

That debate will go on for a while, and these new ad ratings only measure DVR users. But that's where most of the delayed viewing is heading, and at least now there are some real numbers.

So here's what they say:

For starters, 17 percent of U.S. households have DVRs, and among those people, 58 percent watch shows live and 79 percent watch on the same day (meaning, usually, later that night).

Simply, that means one show in five gets delayed at least a day. Meanwhile, 95 percent of the shows are watched within three days.

(Remember, because DVR owners are still a small part of the whole audience, it means that less than 10 percent of all broadcast prime-time viewing is delayed -- for a few hours or a few days -- via DVR playback.)

Now, for ad-watching. This one gets a little weird. And if the numbers don't seem to add up, it's because I'm not very good at math.

In simplest terms, while more than half of DVR users fast-forwarded through commercials, some still watched the ads days later. So -- and this is key -- for many shows, it turns out that the total number of people who watched ads after three days was greater than the number of people who watched the show live.

Here are the numbers: In those DVR households, viewership of an average prime-time show, and just the show, went up 73 percent when you count the people who watched within three days. In that same time, viewership of the show plus ads went up 32 percent.

Other numbers indicate that for a show like NBC's "The Office," which is among the most-recorded, for every 100 DVR users who watched it when it aired in its Thursday time slot, 108 people watched the show -- and the ads -- on a delayed basis but within three days. Those are extra eyeballs for advertisers.

Not all shows got these kinds of delayed-ad-viewing numbers, but many did, including Fox's "Family Guy" and "Bones," the CW's "Smallville" and ABC's "Grey's Anatomy."

What does this all mean to you? Not sure yet. But it does show there is not total "ad avoidance," as they call it in the industry, on recorded shows, and you can guess that the networks and the advertisers are going to spin it differently to try to get the best rates.

Two things, however, are clear. As more people get DVRs, fewer and fewer folks will watch shows at the exact time they are aired. And the TV industry will continue to make big changes and make them quickly -- in the shows they offer, the way they schedule and how they earn their money -- to keep up with the wildly shifting digital world.