The ratio of the distance on the math diary-Viann scale map to the actual distance is called the scale of this map. The most error-prone scale is cm-km. If you convert 50000000 cm into a number in kilometers, you must first convert it into meters and subtract two zeros. This is 50000M m, and if you subtract three zeros from meters and kilometers, it is 50 kilometers. As simple as metric kilometers, we all know that the most hateful thing is the zero inside. Most zeros and a few zeros make big mistakes. Even if the calculation is right, a zero will be all wrong. This is also the easiest place for sixth grade students to make mistakes. If there is a number that is 1.2km, there is no need to add five zeros, because 1.2km is a decimal, and only four zeros can be added. First, convert 1.2km into a number in meters, 120000CM, and now convert it into a number in centimeters.