A timepiece that can be used without sunlight enters the scene

Water clock
Water clock

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Sundials only tell time when the sun is shining, and so water clocks were invented by devising various means of controlling the flow of water to a constant rate. Water clocks were already being used to tell the time at night in Egypt by around 1550 B.C. The oldest existing water clock has a hole in the bottom so that as the water leaked out, the time could be measured by the level of water remaining. To allow the user to read time by a temporal hour system, seasonal time system according to the changes in the length of nighttime through the seasons, the vessel has different scales for each month marked on the inside.

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