《汉书·志·天文志》
在子夜时观测判定时令时是验看衡星，衡星，主预示中原各州地区、黄河、济水之间。
夜半建者衡；衡，殷中州河、济之间。
When observing at midnight to determine the season, Hengxing is used, Hengxing, which mainly indicates the central states regions, between the Yellow River and the Ji River.