eli5 How did Avogadro get the number for a mole?

Question

I understand how a mole works, however, I have no clue how Avogadro got the specific number of 6.02×10^23.

In: 68

Answer 1

1 mole is just the number of atoms it takes such that the atomic weight of the element will be the mass of the whole mole in grams.

Ie 1 mole of helium, 4.002602 amu (atomic mass units) would weigh exactly 4.002602 g

amu and grams have already been established by that point, Avagadro just had the idea of doing chemistry with numbers of molecules rather than masses or volumes of chemicals