第二只手臂没有袖套的束缚，充当对第一只手臂测量时的对照，这样，除袖套对身体的变化有影响外，其他因素均可消除。
The second arm, uninhibited by any cuff, acts as a control against which to assess the first. The effects of changes to the body caused by anything other than the cuff can thus be eliminated.
通过统计所发出X光的数量，然后对照激光脉冲的频率，测量小组能得出一个非常精确的测量值，从2s能级到2p能级跃迁所需的量子能量。
By counting the number of such X-rays while scanning the frequency of the laser pulse, the team could make a very precise measurement of the photon energy required to drive the 2s-2p transition.
“让这些人告诉你他们的饮食结构，然后对这些人进行跟踪研究，直到他们中的一些人患上癌症为止，”Key说道，“因为你在他们健康时就做了测量，所以对照组偏向性就不会产生。”
"They tell you what they eat and you follow them until, inevitably, some of them do develop cancer," said Key. "But you made the measurements when they're healthy, so the biases don't apply."
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