They're all M scopes... My F2 says it on the arm rest
By 1936, sales had increased to the point where the garage was no longer large enough. Fisher Research Laboratory moved to a small building at 745 Emerson St. in Palo Alto. Shortly thereafter, Dr. Fisher was granted a patent for his "Metallascope." The "
Metallascope" was soon nicknamed the M-Scope, and as such, became an accepted standard for all types of electronic metal detection: geologists located ore, treasure hunters found treasure, utility companies located buried pipes, lumber mills located metal inclusions in sawn logs, and law enforcement agencies used it to locate abandoned or hidden weapons.
In 1939, just prior to World War II, Fisher moved to an even larger building at 1961 University Ave. in Palo Alto. During World War II and the subsequent Korean Conflict, the company was called upon to contribute its technical competence to the war effort, but the M-Scope business was never neglected. With the increasing popularity of the M-Scope, and with Fisher’s patent rights expiring, numerous competitors began producing similar equipment. Due to relentless efforts to incorporate every available technical advancement - and in particular, by keeping close contact with countless users to utilize their vast fund of field experience in the design of new models - Fisher maintained its position of solid leadership. Over the years, Fisher has designed and produced such sophisticated products as geiger counters, radio communication systems, voltage detectors and cable fault locators.
http://www.fishermscope.com/company_information.htm