# How were the absolute masses of atoms calculated before the mass spectrometers?

I understand that true (non-relative) masses of atoms are calculated with a mass spectrometer. using this relationship: Centripetal Force = Force due to magnetic field(B)

But I was wondering how masses of atoms were calculated before the mass spectrometers were invented.

(Please don't get this mixed up with relative atomic mass. That's not what I'm talking about.)

Absolute mass can be determined electrochemically, once the coulomb is defined in terms of numbers of electrons, as through the Millikan oil-drop experiment, to be $6.24×10^{18}$ electrons per coulomb.