Kclone, the RS meter's A and C setting "The weighting switch allows for switching between the standard 'A' and 'C' weightings. Choosing the 'C' weighting will make the meter respond uniformly over the frequency range from 32 - 10,000 Hz, and the 'A' weighting will make the meter more sensitive to frequencies in the range 500-10,000 Hz."
I did try both but found little difference. I would think C is the widest and is the normal listening range.