日晷的对应物是水钟，用来测量夜间的时间。
The sundial's counterpart, the water clock, was designed to measure temporal hours at night.
一旦被人所知，它就迅速传播开来，替代了水钟，但却没有替代日晷，日晷被用来将新机器与原来的计时方法进行对照检查。
Once known, it spread rapidly, driving out water clocks but not solar dials, which were needed to check the new machines against the timekeeper of last resort.
在阴天或晚上，无法用太阳钟或日晷看出时间。
On cloudy days or at night it was impossible to tell the time with a sun clock or a sundial.
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