It's neither people use centuries and decades every where
It is customary.
A "gran" is a German measurement, it is neither customary or metric. A "gram" is a metric unit.
metric and customary
metric
They are both systems of measurement except that the metric system is simpler and used by the majority of the world.
No a quart is a customary measurement for the capacity of liquid as where a Kilometer is a metric measurement for length
using classical rather than metric units of measurement
There are thousands of measurement units in both systems and it is not possible to list them all.
No. Century is a measurement of time. A century is 100 years
It is a customary unit.
The MKS-ISO metric system and the CGS-ISO metric system. The American, Imperial, or customary units of measurement are not a system at all, they are an accumulation of antique units.
Feet are a measurement in the Imperial system. If she was using Metric it would be in meters, not feet.