This maximum weight conventional wisdom has become ingrained in the collective psyche.

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So the only sensible material for reducing a conventional car's weight while maintaining its strength is aluminium.

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The ceramic brake discs are 40 percent lighter in weight than the conventional, grey cast iron brake discs.

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But, according to Greg Yurek, American Superconductor's boss, it will be a third of the weight of its conventional alternative.

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Weight Watchers, which promotes conventional diet plans with its own celebrity, Sarah Ferguson, Duchess of York, has seen a 6% fall in Americans attending its slimming programmes.

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The growing weight of the stockmarket certainly suggests that conventional measures of the tightness of monetary policy may be misleading.

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They cannot bear to risk such capital losses again, so they stay away from equities and over-weight their portfolios with Treasury bonds and other conventional fixed income securities where they naively believe they cannot lose principal.

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The pound-and-a-half weight of a current iPad sheds the tremendous amount of weight that would normally be needed for a conventional in-flight entertainment system built into the headrest, which on a typical 375-seat 767 could see the iPads pay for themselves within years, if not sooner.

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So if a patient asks for help with their weight problem, most GPs have little to offer beyond conventional diet for the person who needs to shed 10-15lbs (4.5-6.8kg), or referral for surgery if there is a need to shed, say, more than five stone (31kg).

BBC: GP practices 'need obesity specialists'