This circuit changes the output proportionaly in responds to the change in input frequency. If you adjust the input period (sweep time) to 1ms the output will change the frequency of the output. Adjust the input period (sweep time) to 10 ms and the output frequency changes to as well. I found for this arrangement the circuit works best with input periods from 1ms to 10ms. If this meter was analog it would increase and decrease linearly as the input frequency changes. The potentiometer is used to calibrate the meter for a linear style meter.
