It's about the numerical value of these constants. The 1.673E-27 of the proton and the 9.109E-31 of the electron are completely arbitrary, but their ratio 1836

It's about the numerical value of these constants. The 1.673E-27 of the proton and the 9.109E-31 of the electron are completely arbitrary, but their ratio 1836 isn't. Besides, you can't really measure dimensional values. An experiment to measure the mass of the proton really is a complex way to measure the ratio of the mass of the proton to the mass of the international prototype kilogram; and that's a dimensionless value.