Does anyone know the origin of the ruler?

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Another sign of Lu Ban's invention is that he can correctly draw a right triangle, also called a class ruler, and can tell craftsmen which sizes are irregular and which ones are unlucky according to the rules of divination (geomantic omen). These rulers are still available in Hong Kong today. Lu Ban attached great importance to the invention of the saw. Or inspired by a blade of grass with a toothed blade that cuts your finger, or seeing a cricket cut and eat food with its sharp teeth and leave. Anyway, most of them are described like this. Luban and craftsmen were asked to cut down a lot of wood. After chopping for several days, they were exhausted and their axes were dull. At this time, Lu Ban suddenly cut his finger by a blade of grass. He immediately thought: It must be a good way to make a tool for cutting wood. He chose a bamboo and cut a row of teeth on its edge with an axe. This new saw cuts bark easily. When he sawed the tree horizontally back and forth, the soft bamboo teeth were quickly polished. However, this proves the principle that a saw can cut wood. So Lu Ban put down his hand and went to the blacksmith to prepare an iron plate as hard and sharp as an axe, and then made it into a tooth shape. With this first-hand saw blade, Luban can use it to cut wood accurately and effortlessly on the wooden frame.

Origin and error of rice

1 m should be one tenth of the distance from the pole to the equator. But 1 meter is actually not that long.

Award-winning science reader Ken? Alder said in a book that two French astronomers who were ordered to calculate the length of 1 meter in the 8th century made a small mistake in the calculation, which made the L meter shorter than the actual distance by 0.2 mm. Worse, the two scientists knew that they had made a mistake, but because they didn't know how to correct it, they covered it up. In other words, this mistake has been preserved to this day.

1792, the French Academy of Sciences decided to create a universal unit of measurement: this unit will be one tenth of the distance from the North Pole to the equator. To this end, two French astronomers set out from Paris and walked in opposite directions. They want to measure the distance from Dunkirk to Barcelona via Paris.

Delambre, who is well-read, goes north, while she is meticulous and beautiful.

Once they reached their destination, they began to measure the distance between them. In seven years, the footprints of these two scientists crossed the land of France ravaged by the revolutionary war. Delambre was lucky enough to escape from the guillotine on the outskirts of Paris, while Shangmei was once trapped behind enemy lines and was banned in the Franco-Spanish War.

However, the two finally met in the southern fortress of Carcassonne. From there, they returned to Paris and gave the information they obtained to an international committee. People greeted them like heroes and made a l-meter-long pure white gold pole to commemorate their calculation results.

Napoleon, then the new ruler of France? Bonaparte said: "Victory is like passing clouds, but this achievement will last forever."

However, no one knows that Shang Mei discovered his calculation error, but he covered it up. It was this sense of guilt that made him die prematurely.

In his book The Measure of Everything, Dr. Alder said that Shang Mei found that the readings he got from the same place in two summers were not consistent. According to modern satellite measurements, the meridian length from the pole to the equator is 10002290 meters.

Dr. Alder said that this error was caused by slight wear on the surface of the measuring instrument.

Shang Mei's letter shows that he almost went crazy after discovering his mistake. In order to correct this mistake, he made another trip. Finally died of malaria.

Alder thinks that Shangmei may be too hard on himself, and the goals he and Delambull set for themselves are almost impossible to achieve.

He said: "Fundamentally, they made the wrong assumption that the earth is a regular sphere. Facts show that there are ups and downs on the surface of the earth. "

/Class3 10