Mass is not weight -- True or false?

Mass is an inertia measurement and a quantity of matter? If we put two different masses on a see-saw they balance at different distances from the fulcrum. Now if we increase their size by the same amount, they still balance at the same distance from the fulcrum.

Conclusion? Mass is independent of size and size is an amount and therefore mass is not a quantity of matter -- Sir Isaac Newton erred.

Further conclusions:

Relativity matters: there is no absolute mass. Measurement is the building of a set that compares the elements of the set. The correct set and not just any set is required.

Mass as an inertia measurement or comparison is correct, and mass as a quantity of matter is incorrect.

Is mass: mL-squared = mL-squared on a see-saw? Or is mass the weight because 'a' in W = F = ma is 'g' a constant on each side? And so mL =mL?

Now I beleieve a FMMC electrical meter measures the inverse of mass in its needle-deflection amount. Therefore someone could find a way to correlate the two and show the meter measures mass and show how the see-saw measures mass. (Of course there are other ways to measure mass.)