The correct explanation for why moving the decimal point left or right works for converting measurements in the metric system is: The metric system is based on powers of 10.
This means that each unit is either 10 times larger or smaller than the one before it (e.g., millimeters to centimeters, centimeters to meters, and so on). When you convert between these units, you are effectively multiplying or dividing by powers of 10, which translates into moving the decimal point either to the left (for larger units) or to the right (for smaller units).