However, after the experiment described above the difference in time between the two clocks was less than a billionth of a second, which is why very accurate clocks were needed.

但是经过上述实验后，两个钟表的时间差距不到十亿分之一秒，所以需要用两个非常精准的钟表。

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The TM set of equations can be solved using a finite difference time domain (FDTD) approximation that is second-order accurate in both space and time.

采用时间和空间均为二阶精确的有限差分方法，将偏微分方程进行差分化。 这样，空间的电磁场可由时间域有限差分法（FDTD）来求解。

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