So 82 was the line in the sand? As the yen approached that level on Wednesday morning, strengthening to 82.88 against the US dollar, finance minister Yoshihiko Noda gave the order. Heavy yen selling ensued.

The immediate benefits were obvious. By the time trading was under way in New York, the yen had dropped 3.4 per cent, reaching 85.7 to the dollar. Equities roared; only eight stocks on the Nikkei 225 fell for the day. Gains were led by carmakers Mazda, Toyota and Fuji Heavy Industries, producer of the Subaru, which had been among the most vociferous supporters of intervention.

Longer-term, though, the outlook is murkier. The yen is still stronger than it was just over a fortnight ago; further weakening may require collusion with the Federal Reserve and the European Central Bank, which seem quite happy with their currencies where they are. Traders are understandably sceptical that the BoJ will be able to keep the yen down in these circumstances. Japanese exporters may now make a little less noise about uprooting domestic production, but they were doing that anyway, while the yen was much weaker.