The difference between the heights of 2.9 meters and 3 meters is in the sand spring.

Phase difference 10 cm. The height of Shaguang Spring is 2.9m, with 3m difference 10 cm. "m/m" (mètre) is the basic unit of length in the international system of units, with the symbol m, and one meter is equal to 10 decimeter. It can be used to measure length, width and height. The definition of "meter" originated in France. The length of 1 meter was originally defined as one ten thousandth of the distance from the equator of the earth to the north pole on the meridian passing through Paris, and then the international meter origin was determined. With the deepening of people's understanding of measurement, the definition of the length of meter has been revised several times.