古代有一种用来测量日影、校正四时和测度土地的器具叫“土圭”。一看这个名称,好多人认为是用泥土制成的。连英国的中国科技史专家李约瑟先生也说:“测日影长最初当然是用当时的尺,但由于尺的大小随官方规定和地方习惯而有不同,因此特制了一种可称之为‘表影择板’的标准玉板,也就是土圭。《周礼·考工记》中提到过土圭。用赤土制的实物现在还存于世,有 In ancient times there was a device for measuring the shadow of the sun, correcting the four o’clock and measuring the land called ”Tugui.“ A look at this name, many people think it is made of clay. Mr. Joseph Needham, a specialist in Chinese history of science and technology in the United Kingdom, said: ”The length of the measuring shadow was, of course, initially ruled at that time but due to the size of the ruler being different from the official rules and local customs, The standard jade board of the “watch selection board”, that is, Tugui, was mentioned in “Chou Kao Gong Ji”