Cash and carry

Foreign exchange

Making money from currency movements is notoriously difficult. Foreign exchange analysts at the world's top investment banks, with a mass of flow data, sophisticated models and comprehensive economic analysis at their fingertips, are often off the mark with their predictions of where spot rates will be in one month or one year's time. Retail traders, with little to go on but guesswork, are likely to fare much worse.

But in the decades since the 1971 collapse of the Bretton Woods agreement, which