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According to Needham, the earliest development of the armillary sphere in China goes back to the astronomers Shi Shen and Gan De in the 4th century BCE, as they were equipped with a primitive single-ring armillary instrument.
This would have allowed them to measure the north polar distance ( declination ) a measurement that gave the position in a xiu ( right ascension ).
Needham's early dating, however, is rejected by the sinologist Christopher Cullen who traces the beginnings of these devices to the 1st century BCE.

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