Wiring voltmeter

[Mobilesport]

I found this voltmeter In a old project I had but I don't remember how to wire it , 
It has four wires
Blue
Green
Black
Red
I think I'm supposed to apply 9 volts to the red and black wires 
Does anybody know what the blue and green wires are for?

 

[Optimistic Paranoid]

With a four wire voltmeter, two of the wires would go to the power supply or battery, and the other two would hook to the circuit you're trying to measure . . .

 

[Mobilesport]

With a four wire voltmeter, two of the wires would go to the power supply or battery, and the other two would hook to the circuit you're trying to measure . . .

Thanks for replying ,