1. The voltmeter has simple wiring. It usually uses two wires, red for positive and black for negative. It has reverse connection protection, so it 't burn if connected in reverse. 2. It doesn't need an external power supply. It can work directly with the measuring voltage. The measuring voltage range is 2.4V-32V for two lines. 3. It works with a wide voltage. The minimum measuring voltage of red is 2.4V, and the maximum safe pressure can reach 40V. It may be if it exceeds 40V. 4. When measuring voltage below 10V, two decimal places are displayed; when measuring voltage above 10V, one decimal place is displayed. Measuring range: Two-wire DC2.4-32V Power supply range: No need for separate power supply Test voltage Test accuracy: ±1% 10V error plus or minus 0.2V Less than 10V plus or minus 0.03V Input impedance: 50KΩ Working current: Less than 30mA Refresh rate: About 100mS once Display specifications: Three-digit 0.36LED digital tube Lead length: Default 15cm Opening size: Hole spacing: 28mm Aperture: 2.8mm Working temperature: -10℃ - +65℃ Working humidity: 10%- 80% Working air pressure:80kPa- 106kPa Note: Installation guide not included, we strongly recommend you professional installation. Please check as much as possible to make sure the item is what you need. Tips: The product may be updated constantly ,Due To Different Batches, The Actual Product May Have Slight Differences Or Color Differences, Which Does Not Affect Use Colour:Photo Color Material:plastic Package Contents: 20 x Mini Digital Voltmeter Only the above package content, other products are not included. Note: Light reflection 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.