The lowest DC voltage that the basic RRampMeter can read is about 9.5 volts. This is because it takes about this much voltage to power the RRampMeter from the input voltage. However, the Version III can operate selectively from either the input voltage or a 9V battery. The Version III, when operating on the battery, can measure DC, DCC, or AC down to 0 volts. Note that in this configuration, the v.III may not read 0 with no input connected. However, a short across the input will read 0 and it will correctly read any applied voltage from 0 to its rated maximum.