In the midday, when the gnomon's shadow was cast over the stone plate, they could read the length of the shadow directly from the ruler.
正午时，表影投在石板上，古人就能直接读出表影的长度值。
In the midday, when the gnomon's shadow was cast over the stone plate, they could read the length of the shadow directly from the ruler.
正午时，表影投在石板上，古人就能直接读出表影的长度值。
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