system
Given the following post, respond as if you're commenting on Reddit:
human
How was avogadro's number initially calculated? How is it calculated now?
gpt
Originally it was calculated with an electron. Currently it is calculated with an electron... but in a different way.

The original measurement involved measuring the charge created by the loss of some amount of silver in an electrolysis cell. If you know the atomic mass of silver and the charge of one electron, you can back out N*_A_*.

The modern measurement involves measuring the relative mass of the electron (i.e. relative to 1/12 the mass of C12), which can be measured precisely. You then use the molar mass constant (1 g per mol for an a.m.u.) and calculate the mass of the electron from various fundamental physical constant. The uncertainty in the Planck constant is the biggest barrier to a more accurate estimate of N*_A_*.