Camco's 120V RV AC Line Voltage Meter is designed to plug into any 120V residential wall receptacle and provides a continuous, accurate reading of your AC line voltage. The meter can be left permanently plugged in and helps prevent costly appliance repair bills by warning against "brown-out" conditions. It is ideal for use on boats, RV air conditioners, generators, computers and campgrounds. This product features a simple to read colored scale. The green zone on the scale indicates proper levels; if the meter reads in either red zone, voltage sensitive appliances should be turned off to protect against damage. Please note that the acceptable voltage operation range varies with the appliance type/manufacturer and you should consult with the appliance manufacturer for the recommended voltage range.