RioRand Small Little DC Digital Voltmeter 2-Wire 0.56" DC 3-30V Green Bright LED Car Motor Panel Mount Voltage Meter 5V 12V 24V 27V Solar Battery Volt Accurate Power Monitor Gauge Powered by RioRand Advanced Technology Measure DC 3-30V directly (two wires Access), do not need extra power source Precision automatic adjustment: Measure 10V Below, Display as x.xx; 10V Above, Display as xx.x 0.56" Digital Tube with Big, bright Green LED display. Perfect for solar project to monitor Battery voltage. The power consumption is &lt;=12mA when in use Very nice to check the voltage and charging system on cars. There is a small calibration adjustment