请注意，在一个封闭的宇宙你可以朝着一个方向开始旅行，如果允许足够的时间，最终将返回到出发点；而在一个无限的宇宙中，你永远不会回来。

Note that in a closed universe you could start a journey off in one direction and, if allowed enough time, ultimately return to your starting point; in an infinite universe, you would never return.

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如果获取读数前允许的时间等于上升时间，将会产生大约10%的误差，因为信号只能上升到其最终值的90%。

If the length of time allowed before taking the reading is equal to the rise time, an error of approximately 10% will result, since the signal will have reached only 90% of its final value.

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