I have installed a balance type ammeter in the prop circuit as is being discussed here.
In the attached photo of my engine/prop control cluster you can see that the prop control is labeled, not the meter. The meter is installed vertically and deflects in the same direction as the control switch so there is no need to label the meter since it is just a visual reference to assure that when you deflect the control that something is actually happening.
This has already saved me lots of time troubleshooting when the prop adjustment is not working.
Jim

Ed Anderson <eanderson@carolina.rr.com> wrote:
Buley, Just so you have the frame of reference firmly in your mind. For
example, you could either have the amp meter labeled with the first order
effect - Lower Pitch /Higher Pitch or second order effect Higher
RPM/Lower RPM. Since it is engine rpm that I would be primarily interested
in, I (if I had a variable pitch prop) might label the meter with Higher
RPM/Lower RPM or perhaps Increase RPM/Decrease RPM rather than lower
pitch/higher pitch (the latter requires some mental manipulation). Just a
point of view.

Ed