@lewm , I looked into static electricity meters. The ones used in industry are very expensive and hard to justify. Charge levels that are not painfully obvious are of little consequence. I have found subjective findings good enough for our purposes.
I am fortunate to have a wonderful static generating machine, the vacuum clamping mechanism of my turntable. On removing untreated records from the platter you can see the sparks jump if the lights are down as well as hear them. The grounded sweep arm will discharge to upper surface but not the lower one. This led me to develop a record cleaning solution that prevents the formation of static. It works a treat as the British would say, but it is only appropriate for use with vacuum cleaning machines. Air drying will leave too much residue on the record and you will see it collect on the stylus. Vacuum drying leaves so little the stylus remains clean. I also think the records are quieter after treatment. Once I get my act together I'll make before and after files for comparison.