What is the purpose of having the millimeter and the kilometer?

Answer 1

The bigger question is the purpose of the mile. The kilometer is 1000 meters (which is the standard unit of distance). The mile is mainly used in America. Most places outside the US use their the kilometer when referring to distance travelled. There is about 0.621 miles in kilometer. The same is true with the millimeter. There is 1000 millimeters in one meter. There is 2.54 centimeters in 1 inch (therefore, 25.4 millimeters in an inch). The inch is again, a US measurement.

The purpose of the standardized units was two-fold.

1) They were created as a universal measurement that everyone in every country could use to quantify weights, distances, etc. People wanted a number for how much they weighed, or how far they travelled. Standardized Units were created so that when you say you weighed 70kg, it meant the same everywhere. If you go some places and say you weighed 154 lbs, they might not know what a pound is.

2) To provide faster easier conversions between measurements. For instance, everything is a nice, neat base 10 in standard units. A millimeter is 1/1000 of a meter, a centimeter is 1/100 of a meter, a decimeter is 1/10 of a meter. And when measurements get larger, it is easier to say "The distance from point A to point B is 1236 kilometers," instead of, "The distance from point A to point B is 1,236,000 meters." In the US, for instance, we say there is 5280 feet in a mile. That isn't as simple as moving a decimal point around and/or adding zeros.