Calculators, cellphones, faxes, televisions, VCRs and watches were among the gadgets criticised by Harold Thimbleby, an expert in human-computer interaction, in his inaugural lecture as professor of computing science at Middlesex University, writes Tony Durham.

In the cause of knowledge Professor Thimbleby has immersed himself in the workings of everyday gadgets and distilled their intricate and often baffling behaviour into flowcharts and logic specifications. Whenever he sees a new calculator he is tempted to test its per cent key. On different models, entering "1+5%" can give half a dozen different answers.

On some gadgets it requires phenomenal amounts of button-pushing to make anything happen at all. It takes an average of 12.3 button presses to actuate one of the Motorola mr20 cellphone's 105 functions. To search through all the functions to find the one you want may require as many as 206 button presses. Professor Thimbleby suggested several ways the product could be redesigned to make it simpler to use.

Unfortunately, simplicity does not sell. Professor Thimbleby showed a range of digital multimeters.

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"You will notice that for another Pounds 10 you get another button," he said. He used a flowchart to show that the extra button was unnecessary and potentially confusing.

"These buttons are not to make it easier to use," he said. "They are made to make it easier to sell."

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The manuals that come with the gadgets are often blamed, but Professor Thimbleby argued that "it is impossible to write a good manual for a bad gadget." Manufacturers should try writing a short, clear manual first and then design a gadget which works exactly as the manual says.