《宋史·列传·卷五十二》
张咏上疏说 ：昨日经过利州时，那里用一枚铜钱换五枚铁钱，在绵州则一枚铜钱换六枚铁钱，在益州则一枚铜钱又可换八枚铁钱。
咏上言： 昨经利州，以铜钱一换铁钱五，绵州铜钱一换铁钱六，益州铜钱一换铁钱八。
Zhang Yong memorialised by saying: When I passed through Lizhou yesterday, one copper coin could be exchanged for five iron coins there; in Mianzhou, one copper coin could be exchanged for six iron coins; and in Yizhou, one copper coin could be exchanged for eight iron coins.