DDS-3X25 USB Frequency/Counter Measurement Click the “F/C ON/OFF” to turn on or off the frequency/counter measurement. Input the signal through the “COUNT IN” terminal, and turn on the “F/C ON/OFF”, you can see the measured frequency value in the edit box. Turn the left-right button to “C” end; you can see the counter value in the edit box. DDS-3X25 USB User’s Guide 24