What is this VU-meter?
To combine a lot of the comments...

That's a VU meter.  It has a highly non-linear scale, marked in decibels.

It looks like a normal moving coil meter, in which case it will work on DC, and the full-scale deflection is probably a few tens or hundreds of microamps.

If you really want to use it, you'll need another accurate voltmeter to calibrate it against.  You'll first need to work out what series resistor to add to make it read full scale at the maximum voltage you have.  This may be tens or hundreds of kilohms.

Then open the top, and replace the scale with a new paper one.  Carefully mark it at different voltages, as measured by the other meter.  Then take the scale out, mark it up neatly, and put it back in again.