(FORTUNE Magazine) – Hey, remember the Decoder Circuitry Act of 1993? No? Well, thanks to this little-known law you can follow Friends while on the treadmill or track CNBC in a busy office. The act mandated that all TV sets larger than 13 inches be equipped with a chip that allows you to view closed captions. That has turned out to be a boon not only for the hard of hearing but also for gyms, restaurants, bars, and offices, where the blare of a TV might be unwelcome.

When the networks, which pay for the service, need to find someone who can type as fast as John Madden can talk, they often look to Canonsburg, Pa. This is home to Vitac, one of a handful of firms specializing in closed captioning. Vitac employs 130 captioners, of whom 25 can do live captioning. Many of these specialists are former court reporters--which stands to reason, since captioners use the same keyboards.

The key to speedy transcription is to type in syllables rather than words, and to do so phonetically. An electronic dictionary translates such keystrokes into words, which appear on the TV screen within a few seconds of being uttered. Good captioners can transcribe 250 words per minute, which is well above the speed of normal speech.

For common words and phrases, captioners save time by devising abbreviations. Kathy Robson, who captions newscasts and sporting events, has added the abbreviations LAUNS for Lewinsky and MAUNS for Monica Lewinsky. The specialized dictionary can also be used for the opposite effect: to make vulgarities difficult to type by accident. Which is not to say accidents don't happen. Robson admits that in keying in an obituary for Audrey Hepburn that said she'd "played with some of the best leading men," she inadvertently lopped the p off played.

Still, Vitac President Joe Karlovits maintains that his live captioners have an accuracy rate above 98.5%. And thanks to new laws requiring all shows to be captioned by 2006, Vitac's business looks set to continue its current growth rate of 25% a year. But investors looking for Internet-sized returns are out of luck: Vitac is privately held.

--Tim Carvell