《明史·志·卷一》
《周礼》记载了圭表、壶漏，但是没有记载璇玑、玉衡，它的形制便不能够考察了。
《周礼》有圭表、壶漏，而无玑衡，其制遂不可考。
The Records of Rites contains the armillary sphere and water clock; however, it doesn’t contain Xuanyi and Yu Heng; therefore, their forms can’t be investigated.