>>470403Since length is arbitrary the metre is a unit which does not have a scientific base, it was chosen. The base for it is the average circumference of the earth, they then chose it the way that 1m is 1/10000000 of the circumference bewtween the pole and equator so that earth has a circumference of 40000km. in the metric system everthing is based on powers of 10. there are several powers which are named by using prefixes, for example 10^3 = 1000 = kilo, so 1000m = 1km, 10^-2 = centi, 10^-1= deci etc.
Today this definition of the metre is obsolete and was replaced by one being dependant on the speed of light, since that one is always constant
Weights are based on the weight of a base artifact which was defined as 1 kilogram, it is a cylinder of metal of which then several copies were made and these prototypes then given to the countries which they used to calibrate scales. It is not arbitarily chosen however, it was based on the volume of water at specific circumference, 1kg was the weight of one liter = 1 decimetre^3, a cube of 10x10x10cm at specific conditions, since these are very difficult to always have exact, temperature, pressure etc... they switched to the prototype solution. 1/1000 of a kilogram is 1 gram, 1000 kg are a ton.
The kilogram and all units based on it is the last unit based on a prototype and not scientific constants.
For temperatures there is the Celsius scale, 0° is the point at which water freezes, the second point is where it boils, both under exact pressure conditions, the scale was then divided in 100 parts since that number is easy to handle and again is a power of 10, of which each is one degree.
