Japan should leave its currency bazooka at home

Robert Rubin, the former U.S. Treasury secretary who added American firepower to the successful defense of the yen in the late 1990s, had some rules for foreign-exchange intervention. Such moves needed to be very rare and ought to be startling. The more surprise, the better, because a market whose value has swollen to $7.5 trillion a day could easily swamp such action.