One of the intimidating aspects of TV advertising is the language. The medium has a slightly arcane vocabulary that spoken rapidly can obscure rather than explain.

At the heart of the language used by those working in the industry are two key words, reach and frequency. Thus a campaign could be described as reaching "80 per cent 1+ cover" or in layman's terms four-fifths of the target audience would have seen the ad at least once.

Brands have adopted a variety of approaches to reach and frequency. From Lynx's recent "Spray More, Get More" World Cup ad that was broadcast on terrestrial TV just once on a single high reach occasion - although online viewings and PR helped drive total reach - through to Crazy Frog's decision to pummel away in a more targeted environment until we were all heartily sick of it.

Although all campaigns are set up on a bespoke basis with precise reach and frequency targets determined by factors such as sector, the stage in the product lifecycle, competitive activity as well as the budget, it's still possible to discern a number of basic reach and frequency models.

Kathleen Rigg, joint head of TV at Initiative, says the first stage of the process is often to look at the factors that help you determine how many times your ads need to be seen to generate an effect on the consumer, say three to five or four to six, for example.

Factors to consider include the power of the creative, the objective and the competitive context of the campaign. "As a result of that process you come out with a frequency objective," she says.

There are also some limits to how low frequency can be. Rigg argues that a sale or promotion in which a simple and easily understood message is conveyed might work at such levels. "You may only need to see such messages twice over a short period of time," she says.

Nevertheless for more complex messages this is generally too low. "If you looked across our clients' businesses most use a 3-5 as a frequency range perhaps four to six," says Richard Oliver, managing partner at Universal McCann.

"When you start getting down to the level of one to two, I think you are really starting to challenge the norms of TV advertising. If people are asking the question how low can you go, what it tends to mean is that they fear they can't do a conventional TV campaign," Oliver says.

DR TV strategies often opt to reduce their reach in favour of higher frequency or more drawn-out campaigns. By cutting back on the size of the audience you can use cheaper dayparts and channels to provide low cost frequency.

"Given there's a diminishing return there's a limit to how many times you're going to want to put it out in any one week," says Rigg. "Increase your weight above a certain level and you're basically just increasing the weight for the heaviest viewers."

A similar strategy is used to limit reach to a specific core target audience such as kids for example by restricting daypart, programme choice and channel choice. "In such cases core target audience coverage and affinity becomes far more important than overall coverage," she adds.

And despite all the gloom and doom surrounding media fragmentation TV experts all contend that the much-reported death of the mass-market campaign is still some way away.

"It's still absolutely viable to buy a big reach campaign," says Oliver. "A well bought campaign will have 2-3 points less of reach at most compared to one you could have bought five years ago."

OMD head of television Neil Johnston agrees that the drop is pretty marginal. "Four hundred ratings do not get 80 per cent you get 76 per cent. The reality is that it's still fairly easy to get high levels," he says.

In recent years the way that planners and clients approach reach and frequency have changed. Notable shifts include the move among FMCG clients away from a regular burst of activity in favour of a more all-year presence.

"A huge number of clients are on a recency model, using TV far more consistently through the year and at lower weights than they would have been five to ten years ago," says Oliver.

"FMCG used to do four weeks at 400 ratings and with a media budget of £5m did four of them a year, there's less of that now. People do try and make their money go much further and try and have more days on air," adds Johnston.

Another sector that's also adopted a similar approach is the automobile sector, which after years revolving around number plate changes twice a year has adopted a new approach. "Now it's a 52-weeks category with reasonable high weights and consistency with far more of a portfolio approach," says Oliver.

A further change is the move towards more tightly defined target audiences. While this might seem an obvious strategy for low budget brands using TV for the first time, it's also been adopted by some of the bigger spenders.

"Ten years ago you might have talked about a product being for ABC1 adults, now I'll see a plan targeting ABC1 adults aged 35-45 with kids. "We are doing much more narrowing of the bullseye audience," says Johnston. "Cars are getting more niche as well. Ten years ago Ford made a Fiesta, an Escort, a Mondeo and a Scorpio, now they make about 10 different cars."

For some brands however the primacy of reach and frequency as the driver of TV advertising is being challenged. "All our media plans will have a reach and frequency, it's still a key element still something that we report but it used to be the be all and end all, the only measure," says OMD's Johnston.

The use of econometric modelling provides a more direct route to proven results and has become a key TV planning tool. A good model will predict the ratings required to generate sales and hence determine the reach and frequency needed.

"We do less planning on a reach and frequency basis than we've ever done in the past because of econometrics," he says. "They start from the principle that they need X weight to trigger the sales response and the by-product of that is you get 80 per cent 1+ cover."