It occurred to me that although I have taught how a moving-coil meter works, I don't actually know what goes on inside a digital multimeter. I've read several articles and I haven't yet got a pithy explanation. I think it boils down to a comparison method of turning an analogue voltage into a digital response. An ammeter would then use a the voltage across a known resistor and I=V/R to come up with a value.
https://electricalfundablog.com/digital-voltmeter-works-types/#How_does_a_Digital_Voltmeter_Work has 5 principles of operation.
https://www.electronics-notes.com/articles/test-methods/meters/how-a-dmm-digital-multimeter-works.php is another good starting point.
