I am pleased to report that I have successfully recalibrated my light meter. It does appear that the potentiometer on the right is a gain adjustment and the left one is offset.
After about 2 hours of work, my built in meter is spot on with my Gossen Luna Pro F throughout the full range of illumination. My Luna Pro was just calibrated by Quality Light-Metric in Hollywood. I highly recommend them.
So it can be done.