《明史·志·卷七》
测定时间的方法，壶漏是古法，轮钟是新法，然而都不如以太阳和星星作标准。白天用太阳，晚上任选一个星座，都用仪器测量经纬度数，推算得到时间。
定时之术，壶漏为古法，轮钟为新法，然不若求端於日星，昼则用日，夜则任用一星。皆以仪器测取经纬度数，推算得之。
The methods for measuring time: the pot leak is the ancient method, the wheel clock is the new method, but both are not as good as using the sun and stars as the standard. During the day, use the sun, and at night, choose any constellation to measure the longitude and latitude with instruments to calculate the time.