Uwe Langmesser wrote:

Is there a simple relationship between a meters internal resistance and
its
sensitivity (ohms per volt).

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Yes. Couldn't be more simple.

It is the internal resistance of the meter divided by the voltage range the
meter is set to.

When the meter is at full-scale deflection the current flowing through the
meter is always (Voltage Range) / (Ohms per Volt).

The internal resistance of the meter, on any voltage range, is the
resistance of the moving coil plus the series meter-multiplying resistance.
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Reg, G4FGQ