The Reliance Controls MB75 Wattmeter Box is designed to give you an accurate reading of how much of your portable generator's power you are using. Knowing this information can come in handy when you are trying to balance the load on the generator, or when attempting to figure out the generator's fuel efficiency. Since 1909, Reliance Controls Corporation has contributed more innovations than any other single manufacturer and has been awarded over 85 patents on manual transfer switches, time switches and accessories. Reliance Controls Corporation specializes in the manufacturing of a wide variety of electrical products. The primary product line consists of heavy duty time clocks and controls, generator accessories, transfer switches and transfer panels for portable generators. And after over a century of innovation, Reliance Controls Corporation has built an enviable reputation for high quality, superior engineering and exceptional customer service.