You can easily upgrade the RRampmeter to V3. First, find the silk screen designation for S1 in the center below the display on the top of the board. To the left, you will see a square pad  hole and a round pad hole. This is the input for external power (labelled J3 on the back of the board). The square is the + input, and the round is the - input. You may use a 9V battery, or any 9 - 15 volt DC power source that has NO connection to the DCC system (e.g. a wall wart). Second, you will need to remove the soldered jumper in the right-most two holes of S1. The PWB was designed to use Digikey switch Part Number EG1903 in this location, but you can use any SPDT switch you like as long as you are willing to connect some wires. When you connect the center and right holes together, the RRampmeter will work off track voltage as it does now. If you connect the center and left holes together, the RRampmeter will operate from the external power and will not be dependent on a minimum track voltage. It will also read negative DC voltages. Note that it does not display a sign, so +12.0V and -12.0V (for example) will both be displayed as 12.0.