LM393 is to me familiar from 1970 -1985 when I was a designing Nokia Capacitor Factory devices.
It was then only DIP8 device, now I use SO8 devices, but the operation is same.
This design needs a positive feedback, so that I got very sharp range change.
Without positive feedback LM393 was not working properly just when the both inputs ( + and -) were almost similar.
The meter needs automatic star and automatic range control, but it used very old AD-device ICL7106, which needed two power supply voltages,
but I have only one 3 V battery .
It need to use very little current 300uA when the device was in not working.
It used about 10mA when everything was working.
I have designed these kinds of the devices already many years, but now I have no oscilloscope available.
It was broken,
Here are my memories ( add : )