The door light ruler is Lu Banchi, also known as class ruler, door ruler, door light ruler and splayed ruler. Lu Banchi is a traditional architectural ruler in China, which is used to control the size of furniture and houses. Due to the control of Lu half a foot, it just avoids the resonance frequency band of the secondary wave.
In fact, this Lu Banchi is not a ruler, but a comparison table. 1 half a foot = 1.368 city scale =45.6 cm; Usually the length unit has the "carry system"; For example: 1 ft = 10 inch, 1 inch = 10 minute, which means this is 10 decimal.