This is the principle behind the armillary sphere and the equatorial bow sundial. Jang created new significant designs for water clocks, armillary spheres, and sundials. The Portuguese shield rests over the armillary sphere. Shen is credited with making improved designs of the gnomon, armillary sphere, and clepsydra clock. The flag of Portugal features an armillary sphere. Crowning the top of the clock tower was the large bronze, mechanically-driven, rotating armillary sphere. Hipparchus probably used an armillary sphere of four rings. Armillary spheres were among the first complex mechanical devices. This was placed over an armillary sphere. He wrote commentaries on Euclid and a treatise on the Armillary sphere. The Portuguese shield was kept, being positioned over the armillary sphere. It was intended to serve as an automatic armillary sphere. The basic version consists of only the Portuguese shield over the armillary sphere. The new flag had a white field with a golden armillary sphere. There is also technical literature in the collection, plus similar instruments, such as armillary spheres.