Hong Kong’s dollar peg is tough. In its 30-plus years it has withstood landmark currency accords, two financial crises and Sars, not to mention perennial debate about its suitability. But the world’s longest-running, unchanged currency regime is facing a fresh challenge: its neighbour, the renminbi.

With data on Chinese capital flows slow to emerge, Hong Kong’s peg to the US dollar has become a gauge of just how much the August devaluation has unsettled investors.

Since that shock move the Hong Kong dollar has whipsawed within its narrow band versus its US counterpart. Initially speculation mounted that a weaker renminbi would force Hong Kong to devalue its currency, and this pushed it lower. Beijing’s still-tight control of its currency since the move, however, has eased that pressure.