i guess the trim pot is to zero out the display, which should be zero anyway. Can you give me an ebay example of the meter. I am only finding LED panel meters from 7.5-20v and analog 0-15v meters.R1& R2 are 220k ohm in my setup. No trimpot now though. ebay a 20 Volt DC auto polarity sensing meter. My pack is 160V. A shorted cell will display half the voltage or about 1.65V. Good luck. Dang spell check!