sentences:  With the aid of Wei Pu, Shen planned to make a series of nightly astronomical observations over a period of five years.To allow more accurate astronomical observations and recordings, Shen Kuo improved the technical designs of the rotating armillary sphere, the gnomon, the clepsydra clock, and the sighting tube.Shen Kuo calibrated the standard diameter of the sighting tube's width, hence allowing the observation of the pole star indefinitely (which had shifted since the time of Zu Geng in the 5th century).