Here is the usual drill: US treasurer calls on Beijing, grumbles about renminbi weakness, is tossed a few bones and returns to Washington. So will it be any different for Tim Geithner when he heads to Beijing next week? Investors think it might be. The non-deliverable forwards market, admittedly a rather artificial measure, is pricing in a 2 per cent appreciation of the renminbi over the next 12 months; several brokerages say the same.

Their reasoning comes from the textbooks. China's current account surplus, while waning, is still large. Tentative indications are that money could start flowing back. Foreign exchange reserve accumulation, which virtually vanished for most of the previous five months, reached a chunky $41bn in March. Subtract the main constituents, namely the trade surplus and foreign direct investment, then adjust for assumptions on revaluation and interest income, and that still implies hot money outflows of about $3bn to $4bn. But resurgent equity and real estate prices suggest a reversal of flows is under way. The trouble is that China often uses a different textbook. Allowing meaningful currency appreciation while exports are flagging would run counter to its mercantilist tradition.

Beijing has lately played the helpful global citizen. It has backed off from forex accumulation, launched a mega stimulus and held the renminbi stable against the US dollar when other Asian currencies were flailing. The real effective exchange rate illustrates that point: it has risen 4.5 per cent in the year to date, using JPMorgan's basket of trade-weighted currencies, while flat-lining against the dollar.