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The earliest measurements of the shadow's length were no doubt made with the foot-rules of the time, but as it was realised that these varied according to bureaucratic prescription and local custom, a standard jade tablet (thu kuei), which may be called the Gnomon Shadow Template, was made for this purpose only. It is mentioned in the Chou Li, and actual specimens, made of terra-cotta, one dated +164 are extant.
The moment of the solstice could thus be determined by placing the calibrated template at the base of the post due north for several days around the expected time, and taking noon of the day when the shadow most nearly coincided with it.
The template system was an attempt to overcome the chaos of primitive metrology, and did not persist...In +500 Tsu Keng-Chih made bronze instruments in which the gnomon and a horizontal measuring scale were combined. About fifty years earlier Ho Cheng-Thien had proceeded to more careful observations of the winter solstice shadow.
Originally posted by Essan
reply to post by tauristercus
The 'improved technology' was the discovery of precession and that earth tilts on its axis - something not known to those who erected earlier gnomons. Thus they became more accurate.
btw how do we know the exact angle and position to which an ancient gnomon was set? Or do we presume it was set to the angle necessary to fit our hypothesis?
And does stonehenge fit with 350BC because it was re-erected incorrectly by the Victorians