I put silver-oxide batteries in my Luna-pro with a spacer. Now it reads about correct if I set the film speed about 2 stops slower than the film I'm actually using.

Directions are here:

http://www.graphic-fusion.com/lunapro.htm

apparently there are potentiometers on the circuit board to 2-point calibrate both the high and low scales. However, I'm a bit worried I will mess it up and get the linearity wrong. I figure the meter is probably right on the way it is now. Has anyone ever done this procedure?