So I seen on YouTube and i think the the geocache forum where a guy added one. It is a 10-20 ohm pot if I remember right. The f2 has a fixed resistor that can theoretically unsoldered and the pot soldered in its place. This along with a voltage increase the guy is seeing a few inches more of depth. I am not interested in upping the voltage as of yet but the variable ground balance may be very benifical in my highly mineralized ground.