《宋书·志·卷十三》
顺行时进入虚宿则在行分上减去六，小分上减一百四十七。逆行时走出虚宿则要加。
从行入虚，去行分六，小分百四十七；逆行出虚，则加之。
When entering Xusui while moving forward, subtract six on the line point and 147 on the small point. When leaving Xusui while moving backward, add.