Tell me of ANY bargraph that will give useful indication
when the change is in millivolts, where the voltage being
measured is 5 to 15 volts. The bargraph would be 2 volts
per division.

I think it's rather finer than that. (My Fluke 87 has 51 points.) But no one
(that I know of) makes a DVM with that can display millivolt changes when
the input is hundreds of millivolts.

The purpose of the bargraph is to give the tech an easily interpreted
indication of which way the measurement is tending, without having to
"interpret" the numbers. And it responds much more quickly than the display
can settle.

I have little need for the bargraph display. But it adds little to the cost
of the meter, and it's there when I do.