The reference 6541 'Milgauss' was launched in 1954. Designed to be used by scientists and those working in areas where exposure to high magnetic fields was unavoidable, the watch was guaranteed to resist magnetic fields up to 1,000 oersted. The word Milgauss means 1,000 gauss (gauss being a measurement for magnetic induction). Magnetic fields can affect a watch's accuracy at just 60 oersted, and at 100 oersted the watch will no longer work. The Milgauss overcame the effects of magnetic fields by using anti-magnetic alloys and an iron movement cover to create a Faraday cage.
Recent research has shown that the dial of this reference is made of webbed laminated copper to protect the movement from the magnetic fields, which collectors refer to as a "honeycomb" dial.