The ability to operate a tape measure used to be the most advanced skill required for buying a TV: How big a screen can fit against that wall?

Nowadays, it seems you need a degree in jet propulsion to understand the techno-babble that trips off the tongues of Best Buy clerks: analog, digital and HD; interlaced pictures and progressive scan; 480i, 720p, 1080i; native resolution; DVD; and Blu-ray disc.

All you want to do is watch "Oprah" and "House."

Make no mistake: You're going to have to know this stuff. After Feb. 17, all broadcasters are required to transmit their signals digitally. Blu-ray's recent victory in the High-Definition (HD) format war means the days of the standard DVD are numbered.

You still have time. Even after Feb. 17, people who subscribe to cable and satellite services can watch their old sets, and those who use antennas can buy converter boxes. So your existing equipment will still work -- even that old Betamax player. But when it dies, you're almost certainly going to have to go HD.

And when you do, you'll see dramatic improvements. With the cutting-edge technologies, your favorite shows and movies will look and sound much better.

For all the crazy jargon, the recent advances revolve around a basic achievement: the ability to transmit, store and display greater quantities of the audio and visual information that makes up your favorite shows and movies. It's akin to the difference between the "draft" and "letter" modes on your printer, or the difference between dial-up and high-speed access to the Internet.

In a nutshell it's as simple as the old adage: size matters.

The decision to get a new TV or disc-player is a personal one. It depends on your desires and budget. You always have to weigh the advantages of waiting over the immediate gratification provided by a spanking new rig. If history is any guide, products should improve while their prices drop.

To help you make your choice, here's a primer on the new technologies based on interviews with Matt Frazer, field training manager for Panasonic Consumer Electronics Co., and Patrick J. Hourigan, vice president of network operations in the Carolina Region for Time-Warner Cable.

Q: What's the difference between analog and digital?

A: A traditional tube TV receives an analog signal, just like over-the-air radio; video comes over an AM frequency, sound over FM. The TV converts these wavelengths into pictures and sounds.

Digital systems replace these waves with strings of zeroes and ones, the same coding used on compact discs and DVDs. It offers two chief advantages. First, it offers a cleaner signal. Instead of having to read subtle variations in wavelengths that are subject to distortion, TVs simply decode the ones and zeroes.

Second, digital systems offer much more bandwidth. This is crucial, because the HD signal takes up four times the space to deliver its richer sounding audio and higher resolution video signals.

Q: Can my old TV handle the digital signal?

A: Only if it has a digital tuner (check your owner's manual).

Q: Will I need a converter box to watch digital TV?

A: Most cable and satellite TV companies will handle that for their customers, converting the digital signal back into analog for older TVs. The only people who will need converter boxes are those who use antennas to watch over-the-air broadcasts on analog TVs. The boxes cost about $70. The government will provide up to two $40 vouchers per household, available at www.dtv2009.gov/applycoupon.aspx

Q: Is HD the same as digital?

A: No. Digital is the method used to transmit a signal to your TV. HD is one type of signal that can be sent digitally. In fact, the law only mandates that over-the-air broadcasters convert to digital after Feb. 17. MTV, CNBC, Fox News and other cable-only stations can continue to transmit analog signals.

Q: What is HD?

A: By law, HD must have two characteristics, revolving around "aspect ratio" and "screen resolution."

First, HD broadcasts must use a widescreen, 16x9 "aspect ratio," which mimics modern movie theater screens. That is, for every 16 inches of width, it must have 9 inches of height. A traditional TV, by contrast, uses a "full screen" aspect ratio of 4x3, similar to the dimensions of most movie theater screens before the 1950s. The difference between these dimensions is the reason you see horizontal black bars when you watch a widescreen movie on a standard TV and vertical black bars when watching an analog signal on an HD set.

Second, where standard TV use a screen resoltuion of 640x480 -- displaying pictures through 640 horizontal lines and 480 vertical lines -- HD must use a minumum of 1280x720; true HD is defined as 1920x1080. As a shorthand, only the second number -- 480, 720, 1080 -- is used to define screen resolution.

Q: How does this offer a better picture?

A: To visualize this, turn on your TV and get real close. See all the little illuminated dots. Those are called pixels. Now do some math. A standard 640x480 TV has 307,000 of them. A 1280x720 picture uses about 1 million pixels; a 1920x1080, more than 2 million. The more pixels you have, the sharper the picture.

Now take one more look at your TV. Notice all the tiny black lines between the pixels -- this is dead space that blurs the picture. More pixels means smaller dead spaces, and sharper pictures.

Q: What does the term "native resolution" mean?

A: That's the number associated with the TV -- 480, 720, 1,080. TVs can only display images in their native resolution. For example, 720 and 1,080 TVs will upscale 480 broadcasts to their higher resolutions, turning those 480 lines into 720 or 1,080 lines. This is why standard DVDs look better on HD TVs. A 720 TV will downscale a 1,080 signal to its native resolution.

Upscaling and downscaling are tricky -- some TVs are better at it than others. This is the reason you should ask your salesperson to display various types of signals on the set you might buy.

Q: What's the difference between 720i and 720p, or 1080i and 1080p?

A: The "i" stands for interlaced, which means your TV is showing only half the picture every 1/60th of a second -- first the odd numbered lines, then the even numbered ones. The human brain is an amazing thing; it is able to merge these pictures into a single image so that it's hard to notice your TV's flickering dance.

The "p" stand for progressive scan, which means that your set is displaying all 720 (or 1080) lines all the time.

In most cases the naked eye will be hard pressed to notice much difference between interlaced or progressive scan signals except in some fast-moving live action broadcasts -- especially sporting events and concerts, which can seem slightly blurry in particularly intense periods.

Q: Does that mean that a 1080 TV is better than a 720?

In the abstract yes. As a practical matter, the naked eye is hard pressed to discern differences in screens 50 inches and less. As you move up into larger screens, a 1080's advantages become clearer.

However, no one broadcasts in 1080p. The standard HD signals now are 720p and 1080i. Again, in theory, the 1080p -- which is known as "true HD" -- provides a better picture as it upscales those lesser signals. But only the most discerning viewers will be able to appreciate them.

Q: So the more expensive 1080p sets are a waste of money?

A: Not exactly. Blu-ray players and the recently discontinued HD DVD format offer 1080p resolution, allowing you to experience all the advantages of true HD.

Q: Blu-ray discs look like my regular DVDs, what's the difference?

A: Size matters. Just as a digital signal can carry more information than analog, and an HD TV can display more of it, a Blu-ray disc can store more it.

DVDs are encoded by a red laser that draws relatively fat lines on the disc. The disc can only hold about 8 gigabytes of information. Blu-ray discs are encoded by a blue-violet laser; it draws much finer lines, allowing the discs to store up to 50 gigabytes.

Blu-ray discs can meet the larger storage requirements of the 1080p signal and also have room for advanced audio formats.

Q: Can it play my old DVDs?

A: Yes. And they will look better than ever on an HD TV.

Q: Can I play Blu-ray discs on my standard DVD player?

A: No.

Q: Are the prices of Blu-ray players expected to fall?

A: Yes. Industry analysts expect a $199 model to be available by the holidays.

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