The correct statement should be: "There is such a short moment in history, because of the change of the definition of a physical unit, the square of π is equal to the gravitational acceleration of the earth at that moment."

This is actually a very interesting story. Starting from the definition of "meter" in that year: 1688, Wilkins suggested that the standard length should be determined by pendulum. Then in 1790, the French National Assembly defined "meter" as "the swinging length of a simple pendulum with the first half period of 1 s at the sea level of 45 degrees latitude". At that time, the consideration was "to establish a measurement system regardless of national boundaries based on the length unit determined purely by nature rather than national laws and regulations."

This is the abbreviation of "rice" in those days. However, in 179 1 year, the French Academy of Sciences finally defined the meridian. Because the hospital believes that to keep the basic unit unchanged, it must be based on natural physical quantities. But the gravity on the earth's surface is slightly different, which will affect the measurement of the pendulum.

The simple pendulum period formula used in high school physics,

T=2 seconds, right?

L= 1 meter, right?

So:

The most important thing is:

At that time, not only were the values similar, but the values were quite ~ ~ ~

Well, that's it. ...