The answer is--this goes way back-- it's an old tradition and they used to have to do this by hand.

答案要追溯到很久之前,这是个古老的传统,他们过去用手工计算

耶鲁公开课 - 金融市场课程节选

On the back of the left hand she made out the post horn tattooed in old ink now beginning to blur and spread.

她发现老人的左手背上,刻有着译车号的刺青,不过已经变得模糊。

耶鲁公开课 - 1945年后的美国小说课程节选