Su Song's greatest project was the 40-foot-tall water-powered astronomical clock tower constructed in Kaifeng, the wooden pilot model completed in 1088, the bronze components cast by 1090, while the wholly finished work was completed by 1094 during the reign of Emperor Zhezong of Song. The emperor had previously commissioned Han Gonglian, Acting Secretary of the Ministry of Personnel, to head the project, but the leadership position was instead handed down to Su Song. The emperor ordered in 1086 for Su to reconstruct the "hun yi", or "armillary clock", for a new clock tower in the capital city. Su worked with the aid of Han Gong-lian, who applied his extensive knowledge of mathematics to the construction of the clock tower. A small-scale wooden model was first crafted by Su Song, testing its intricate parts before applying it to an actual full-scale clock tower. In the end, the clock tower had many impressive features, such as the hydro-mechanical, rotating armillary sphere crowning the top level and weighing some 10 to 20 tons, a bronze celestial globe located in the middle that was 4.5 feet in diameter, mechanically-timed and rotating mannequins dressed in miniature Chinese clothes that exited miniature opening doors to announce the time of day by presenting designated reading plaques, ringing bells and gongs, or beating drums, a sophisticated use of oblique gears and an escapement mechanism, as well as an exterior facade of a fanciful Chinese pagoda. Upon its completion, the tower was called the "Shui Yun Yi Xiang Tai", or "Tower for the Water-Powered Sphere and Globe". Joseph Needham writes: