In Joseph Needham's book on ancient China "Astronomy" Page 246, he shows a diagram of the ancient Chinese sky, perhaps 2400 BC. "The apparent exactness of this passage(noon) has long offered to scholars an irresistable invitation to determine its date by the precession of the equinoxes. Thus J.B.Biot was able to show that the four hsiu mentioned would have occupied the equinoctal and solistial points (0, 90, 180, 270) about the year 2400 BC. Indeed, there is not much escape from this conclusion. Maspero in criticising the assumptions involved (the chief of which relates to the hour of observation of culmination), and Hashimoto, assuming 7PM and so reducing the date to -800 or rather later, perhaps hardly gave enough weight to the venerable tradition preserved by Gaubil that transit observations were made at 6PM and checked, if daylight prevented them by, the the clepsydra. But the great difficulty of any exact determination of the date was pointed out a century ago by Pratt. One of the most recent discussions is that of Chatley, who while recognizing the strenth of the case of Biot and de Saussure adds futher uncertainties. The term Niao (Bird Constellation), in its widest sense, can include no less than seven hsiu (the whole of the eastern palace), and Huo(Fire Constellation) can include three. On the other hand, Hsu and Mao, which are individual hsiu of small equatorial extension, agree very badly together, the former indicating a date of about 350 BC and the latter one about 1400 BC. The question is far from settled.."