《汉书·志·天文志》
夏至运行到东井宿，北近天极，所以晷影短；立八尺之圭表，晷影长一尺五寸八分。
夏至至于东井，北近极，故晷短；立八尺之表，而晷景长尺五寸八分。
The summer solstice moves to Dongjǐngsù (East Well asterism), close to the North Celestial Pole in the north, so the shadow of the sundial is short; an eight-foot gnomon is set up, and the shadow of the sundial is one foot and five inches and eight minutes long.