1. Luban ruler, the full name of "Luban construction ruler", is a measuring tool used in building houses, similar to the curved ruler used by craftsmen today. The Luban ruler is about 42.9 centimeters long. According to legend, it was made by Gongshuban of the State of Lu in the Spring and Autumn Period. Later, the eight characters were added through the Feng Shui community to measure the good and bad luck of the house, and it was called the "door meter ruler". Also known as "square", it is a woodworking tool mainly used to check whether the planed boards, planks and structures are vertical and the edges are at right angles.
2. The use of Luban ruler should be coordinated with the construction ruler. The "single door opens two feet and eight inches on the eight whites, and the general ruler is auspicious" listed in the Luban Sutra is to use the construction ruler to make The length of a single door is two feet and eight inches. Press Babai here. Then use the Luban ruler to check it. We use the Luban ruler and line it up one foot at a time. The width of this door just falls on the two feet of the Luban ruler. The last part has the word "吉" on it, so the width of the door is auspicious.