If you want to annoy an economist, try mixing up stock and flow. This is a mistake commonly made even by business journalists (though not Jonathan Prynn, of course) when attempting to describe the value of large companies.
So, for example, Apple Inc has a market capitalisation of $2.6 trillion. But it would be wrong to suggest this is equivalent to the GDP of France. Because GDP is a measure of output – that is, the goods and services produced in an economy. Apple's valuation is mighty impressive, but it is not generating that figure in revenue every year.
