It depends on the meter.
Most panel meters are just a "raw" movement, with a certain sensitivity (usually written on the lower portion of the scale, in tiny text). Typical wording would be "100 uA FS". That meter needs a 100 uA current through it for full scale deflection. Its DC resistance is usually not marked, but can be measured with an ohmmeter (do not exceed the rated FS current when testing). The FS current on a meter movement may have NO relation to whatever the scale markings are. The scale can be printed to read in whatever units you want. The actual meter in an analog VOM is a microammeter. It is adapted to measure voltage, current, or resistance by the external circuitry wrapped around it.
Some panel meters incorporate internal resistors in series or parallel with the basic movement, to create a voltmeter or a higher range ammeter. These usually have a scale that directly corresponds to their input requirement, direct voltage or current input.
To adapt something like a DPM module that needs 200 mV full scale input, you need to look at the circuit and figure out what is being applied to the existing meter. Then adapt the circuit as needed. You may need to add a voltage divider to drop voltage down, or a shunt resistor to develop a voltage drop proportional to current (and that shunt should ideally be close to the DC resistance of the original meter movement).
Once you have a suitable input signal for the meter module, you can calibrate it to read in whatever engineering units you want. by using a trimpot as a voltage divider.
Post some specifics of what you are working on, a schematic would be a good start.