《左传·定公·定公九年》
晋国的战车一千辆在中牟，卫灵公准备去五氏，占卜经过中牟如何，龟甲烤焦了，卫灵公说： 行了，卫国的战车相当于他们的一半，寡人也相当于他们一半，这就相等了。 
晋车千乘在中牟。卫侯将如五氏，卜过之，龟焦。卫侯曰： 可也。卫车当其半，寡人当其半，敌矣。 
The Jin state had 1,000 chariots in Zhongmou. Duke Ling of Wei was going to go to Wushi. Divination was used to investigate how to get through Zhongmou. The tortoise shell was burnt, and Duke Ling of Wei said: Okay, Wei's chariots are half as many as theirs, and I am also half as great. So we are equal.