Give Jeason: si System is accepted by all nations in the world.
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it's very practical, because it's on base 10, so conversion between stuff like meters to kilometer is always just a multiplication with 10 to some power

like 1 km = 1000m (10³m)

or 1 m = 10^-3km = 0.001km

same reason for other SI units.

except time, that's base 60, or 12, or 24. that's more complicated, but there isn't any real competition