This discussion reminds me of the article on digital voltmeters in
"Electronics World" about 50 years ago.

Back then, they were huge, taking up (if I recall correctly) a 3U or 4U
space. The meter they described was a Non-Linear Systems model. Its ADC was
electromechanical, (!) using a relay-controlled voltage divider on a
highly-accurate voltage source to create successively closer approximations
to the input voltage.

There were no commercial LED displays, of course, so the results were
displayed using incandescent lamps to side-illuminate numbers cut into
polycarbonate blocks! (I don't know why NLS didn't use Nixie tubes.)