Guo Pu had written in the Zang Shu that 土圭测其方位，玉尺度其遐迩. It is popular that in the Jin Dynasty and Han Dynasty, when the experts of Feng Shui in Chinese culture measured the level surveying and the orientations, they also used another tool—-Yu Rulers to measure the distance. It is sais that in the Shi Shuo Xin Yu •Shu Jie, the famers in Jin Dynasty had found the Yu Rulers made in Zhou Dynasty when doing farm work. Some of the farmers used it to calibrate the melody of the instruments. Therefore, there are different scales carved in the Yu Ruler. According to the record of Jian Wen Lu, the Yu Ruler had evolved in a tool of Feng Shui.
On this account, the Yu Ruler which was used in the Feng Shui culture in Chinese culture was not only the measurement for the length, but also used as other different references to calculate. It seems like the rulers which are used by the primary children. There are many legends about it in Chinese culture. In the record of Hu Hai Xin Wen, in Yuan Dynasty, a stone tortoise in front of the temple had come into a man’s dream and said to him in the dream that it worked for the Long Wang Gui. It said that it would like to steal the Han Long Jing and Han Long Chi to him for copying. At last, the man really had found the book and the ruler before the stone tortoise next day. From then on, that man had been the expert of Feng Shui and he can predict the fate exactly. These kinds of rulers which are different from the common rulers and can be used in the Feng Shui may be handed down in a large mount. What a pity! The writer does not have seen one.
In modern time, the scholar Luo Xiu in Tai Wan has written a book Zhu Zhai Feng Shui Kan Ji Xiong which has introduced one special kind of rulers which is use to predict the Feng Shui about carves. He had seen the ruler for Feng Shui for the first time.
It is a ruler made of metal like a scissors in eight inches. The expert of Feng Shui instructed him to measure carve with the special ruler. With the help of him, I unfold the ruler into a right angle. I hold the ruler with right hand slightly and use the left hand to support the right hand with a fist. This ruler can not be extended in opposite side but toward the original direction. On the other hand, you can prod the other branch of the ruler in other directions. After about ten foot later, with a strange and mystery strength, the ruler has been oriented the direction where buried with five tombs. And the ruler works precisely as long as we tried. At last, when I came to the five tombs, the ruler has been made into a right angle toward the middle of these tombs under an unpredicted strength. It is easily makes me believe that there is magnetic field in the tombs. However it can be true. If it is true, the compass may be out of control already. As long as you pick up the compass, you may clearly see the pointer in the north or the south. This ruler is as small as a finger. And it is just a rough product. Only when this mystery strength is strong enough, the ruler can swing. What’s more, it always points to the precise direction.
And Mr. Wang Yude believes that this kind of ruler is piece of magnet. It works with the rules of the compass. At the same time, the structure of the ruler is not complicated at all. The common ruler is necessary for the experts of Feng Shui culture. It is said that the famous experts of Feng Shui in Song Dynasty also use this kind of ruler to predict the Feng Shui at that time.