Economists have been particularly surprised by favourable inflation figures in Britain and the United States, since conventional measures suggest that both economies, and especially America’s, have little productive slack. America’s capacity utilisation, for example, hit historically high levels earlier this year, and its jobless rate (5.6% in August) has fallen below most estimates of the natural rate of unemployment—the rate below which inflation has taken off in the past.

请问老师，红字部分的句子中的破折号是什么意思呢，the rate 指的是jobless rate 还是the natural rate of unemployment 呢？below which 是什么从句呢，which指代的是什么？take off要怎么翻译呢？这个红字部分的句子的结构成分都是什么呀？麻烦老师解答，谢谢老师！！！恳请老师详细解答！