Special Report on Office Automation: The most useful tool you can buy: The new generation of fax machines are a must for businesses, writes Steve Homer

A FAX is probably the most useful business productivity tool there is. You might only need it once a week but given the amount of time and worry it will save you, it will pay for itself within six months.

In the past, faxes were expensive and needed an extra telephone line. Now, however, using a fax machine with an existing telephone line is a possibility.

But there are pitfalls for the unwary. Fax machines that operate on one line are designed to work in tandem with an answerphone plugged into the fax.

There are various types of single-line machines; most wait for the answerphone to pick up the phone and listen another fax machine to beep; then they take over the line and receive the fax. Problems with incompatibility between your answerphone and fax may occur. This can happen if your answerphone takes too long to pick up: the fax assumes that you have not set it, so takes the call itself.

With a voice-controlled answerphone you need to leave a period of silence before it will read back your messages; many fax machines interpret this silence as another machine trying to fax a document. This can be overridden on most machines but setting the fax to operate correctly can require much time with instruction manuals.

The most common problem I found is not taken seriously by most manufacturers. I have several phones at home; I cannot tell if an incoming call is a voice or a fax, but my instinct is to answer the nearest phone. If the call is a fax and you have picked up the 'wrong' phone, there is no way to get your fax to accept the document. If you answer the phone attached to the fax machine, there is no problem.

Prices start at pounds 300* for a basic single-line machine without paper cutter (so faxes arrive in one long sheet). Some of the more expensive machines have very useful added features. For example, the Samsung's SF-2500 at pounds 499 incorporates an excellent answerphone. BT's CF90 at pounds 645 and Sharp's UX222 at pounds 509 offer similar features.

One other fax machine deserves special mention. Canon's B-200 at pounds 899 does not use the usual crinkly fax thermal paper. It uses computer printer technology to print on normal office paper. This means that your faxes will not fade or curl and that the machine can be used as a copier. On running cost, there is probably little to choose between conventional and plain paper faxes. The B-200 prints slowly (documents are stored in memory when they are received) and the paper often jammed on the model I tried (Canon assures me this is unusual).

Many businesses, particularly those sending or receiving more than four or five faxes a day, should consider getting a new line and a cheaper, simpler fax machine.

When buying a fax machine, particularly a single-line model, try to test it in its intended setting before you commit yourself. Many companies will allow you to do this, so ask around. And seek a good guarantee. Faxes are complicated things and have a nasty habit of going wrong when you need them most.

*All prices exclude VAT

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