I appended the circuit to show just how simple the meter is even with an added display.? The basic measurement code is in the original article. There are dozens if not hundreds of examples of LCD/OLED interface code for Arduino, not least on the Arduino Forum. ?
I'm afraid this is an old project for me now, I came across the files and thought the principles might be of interest to this group.
So a meter that doesn't drift and has fast cycle times is desirable, but one tied to a computer for readout is not useful and my brain is far too old to learn how to modify Arduino code to add a LCD display to make a portable unit. If someone does, please publish.