A quantity of matter is not a fundamental measure; the measures of the
mass in a quantity of matter are the net force [f] exerted on, and/or
by it, divided by the acceleration [a] that is caused; which is equal
to the ratio of its weight [w], divided by the acceleration of free
fall [g] at the location of the scale on which it is weighed:

For any quantity or mass of matter, anywhere, anytime: These _ratios_
are Constants; called inertia [f/a = w/g]; which may be substituted
for any quantity or mass of matter, anywhere, anytime.

The equations: f = ma, or w = mg are strawmen:

f = [w/g]a, and w = [f/a]g!

Wake up and get a good breath of truth.