Review on Mini 3 Digital LED Voltmeter: Accurate DC 2.5-30V Red Volt Voltage Meter for Measuring Power by Jeff Payne

A bit delicate but functional. All circuits are open circuit, so be careful when installing and handling them. There's a slight calibration setting on the back, which is good as you'll need to tweak it for accuracy. Also, as with any such display, you should use a transparent red filter in front of it to protect the unlit segments from ambient light. Otherwise the display will become harder to read. However, no filter is required in the dark.