THE technical charts show the trading bands for US 30-year bond yields on the left and the Hang Seng Index on the right. Thinner lines represent moving averages. Where the moving average lines cross, the market will often start to shift. In the 30-year T-bond chart, the point labelled '3' indicates a bullish cross in moving averages for eight and 21 week periods. 'This was our first warning,' Christopher Day, head of research at Fimat Derivatives, said. 'Underlying sentiment changes are evident after the moving average crosses.' For the Hang Seng charts, Mr Day noted a 'pattern that is usually self-fulfilling' in trading since late January. 'The pattern warns of reversals and fits the upward break of bond yields,' Mr Day said. In fact, the Hong Kong market opened yesterday with a breakaway gap from Friday's close, opening the day sharply below the previous week's close.