1. According to the cultural relics textbook "Ancient Chinese Architecture" edited by Luo Zhewen of Shanghai Ancient Books Publishing House: the clear ruler is 32 centimeters. Some say that the Luban ruler is a wooden ruler with a diameter of one foot and four inches, which is 45.12 Centimeter. The clear ruler is 31 centimeters, which is said to be one foot four inches four, which is 44.64 centimeters. It is estimated that about 45 centimeters should be correct. The error is understandable because of inaccurate measurement in ancient areas. (One foot in Beijing in the Qing Dynasty was 32 centimeters. Therefore, the Luban ruler is 46.08 centimeters)
2. According to the "Dictionary of Chinese Ancient Architectural Terms" edited by Mr. Wang Xiaoqing, the Luban ruler is also called the class ruler, the door ruler, the door light ruler, and the eight-character ruler. The ruler length is 1.44cm. It consists of eight characters, namely "wealth, disease, separation, justice, official, calamity, harm, and origin", and the range of each character is 0.18 square feet.
3. The Luban Ruler in the hands of Mr. Zhao Chongmao, the former engineer of the Renovation Department of the Palace Museum in Beijing.
The length of a ruler is one foot, four inches and four minutes = 460.8 mm