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Ralph Mowery

In article , says...

I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?

I've got four DMMs and two analogs. The DMMs agree with the other DMMs
and the analogs agree with each other. But the different types don't
agree with each other!

If you are measuring in circuit resistance of solid state circuits, then
you often will.

The analog meter has enough voltage/current to turn on the junctions of
diodes and transistors. The DMM will not have enough to turn them on.

If you have a diode out of the circut and use an analog meter you will
often see a small resistance in one direction and if you reverse the
leads a high resistance. The DMM will usually show a high resistance in
both directions unless you use the diode setting if the dmm has one.