DROK 0.56" Multifunction Car Clock/Time Thermometer Digital 0-33V Voltmeter 3 in 1 MCU Red LED Electronic Meter Power Supply: DC 7-30V ( with anti-reverse protection ) Display: Four 0.56 " Red LED digital tube Measuring temperature: -55 to 125c Measuring voltage: Range 0-33VDC Clock: 24-hour, power off memory function,the battery backup is available 3-4 years