Ferris Instrument Corp 18B No. 307 Microvolter Laboratory VHR Signal Generator before World War II. This Vintage Signal Generator was designed to accurately attenuate a voltage source. We estimate is was made in the early 1940s but it could have been made in the 1930s. It was probably designed to service the VHF police and aircraft radio markets which were developed around world war 2. This vintage piece of test equipment belongs in a museum or in a cool sci-fi movie workshop.