I was reading on Wikipedia about how Pauling electronegativities are determined through
$$ \vert \chi_\ce{A} - \chi_\ce{B} \vert = \sqrt{E_\mathrm{d}(\ce{AB}) - \frac{E_\mathrm{d}(\ce{AA}) + E_\mathrm{d}(\ce{BB})}{2}}$$
At first, I thought I understood this since for an element like hydrogen the meaning of $E_\mathrm{d}(\ce{HH})$ is clear and easy enough to measure experimentally.
But I don't see how I would do the measurement in general. Do I have to make (unstable) diatoms and then try to measure the dissociation energy very quickly? Even the electronegativity for atoms with $Z > 100$ are known which baffles me. How do they measure these dissociation energies?