To be perfectly fair, it was a little strange for the metric system to have a "ton" unit in the first place. Much like a foot or a cup, it's one of those units the metric system is trying to replace, but rather than use megagrams or something else perfectly sensible within the system they already created, they added to the confusion by defining yet another "ton" close enough to the historical units of the same name.
it's because "megagram" and "milligram" are a hassle. With the added bonus of mm/MM being used to abbreviate millions, I'm personally very grateful for tonnes.
>The SI comprises a coherent system of units of measurement starting with seven base units, which are the second (symbol s, the unit of time), metre (m, length), kilogram (kg, mass), ampere (A, electric current), kelvin (K, thermodynamic temperature), mole (mol, amount of substance), and candela (cd, luminous intensity).
It means if you are using SI units "The kilogram is defined by setting the Planck constant h to 6.62607015×10−34 J⋅s (J = kg⋅m2⋅s−2), given the definitions of the metre and the second."
and gram is some random word you made up, with no definition under SI.
The gram is indeed defined by SI to be 1/1000th of a kilogram, it's not a random word I made up.
There is no logical difference between the definition you gave, and an alternative definition that says "the gram is defined by setting the Planck constant h to 6.62607015×10−31 J⋅s (J = g⋅m2⋅s−2), given the definitions of the metre and the second", and then defining 1 kg = 1000 g. Which is why I'm asking what this distinction actually means, if anything.
It meant something that feels more real when the kilogram was defined as the mass of a physical reference kilogram object in a vault in Paris, but that changed a few years ago.
