In article ,
wrote:
If the JPI is coming out soon, it might be interesting to pull the other
meter as well. Connect both of them to a 12 V battery sitting on a
table - with the same gauge and lengths of wire - and see what they
read.

The bench test sounds fine, but the same gauge and lengths of wire part is
kind of silly. If these things are pulling more than a 100 mA, I'd be
surprised. Worrying about the voltage drop along a couple of feet of any
kind of wire you're likely to have laying around is just silly.

#18 copper wire is 7 mili-ohm/ft. If this thing were drawing 100 mA, there
would be a 0.0007 V drop along the wire. The problem reported was one
reading being off by several 1/10ths of a volt. Don't worry about matching
wire gauges and lengths on the bench.

As for a reference voltage source, any reasonable DVM you can buy at Radio
Shack fo $20 will be more than accurate enough for this kind of work.