You need more double wires. Power supply is necessary. Power reverse connection protection. Wide working voltage range. Temperature coefficient: 25ppm/ Celsius Range: 0-33.000V DC Precision: +/-2 digit,0.3% Operating temperature: 10 Celsius~65 Celsius Power supply voltage: 4 to 30V : power + (3.5-30v). Wiring: power, black Measures: (0-33.000v + yellow). Product weight: 15g colour:black Material:PC+ metal size:Type: LED 0.36 inch 5 bit Package Contents: 1 x Voltage Meter 1 x Connecting Cable Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.