C2 filters this output peak voltage to a flat DC for the DVM. R5,R6 scale this voltage for the meter’s 200.0 millivolt range. It goes something like this: 120.0 VAC in at R1; 2.5 VDC at the C2,R5 junction; 120 millivolts DC at the R5,R6 junction; and 120.0 volts on