
The Milgauss model has an interesting history. It was introduced in 1954 for people who worked in environments with strong magnetic fields: power plants, research labs, etc. As you might suspect, that's a pretty small market, further crowded by the IWC Ingenieur, the Patek Philippe Amagnetic, and the Omega Railmaster, all of which had similar magnetic resistance. The Milgauss was the slowest seller in the Rolex lineup, and was sold for about 20 years before being removed from their catalog.
The Milgauss comes in the new, slightly larger case size of 40mm, with the 3131 movement. There are white and black dial versions available, both with a nifty and surprisingly modern lightning shaped second hand and 'ROLEXROLEXROLEX' around the face on the chapter ring. (As Christian noted, for better or worse, the new models are more heavily branded than their predecessors.) One difference between the two versions is that the black dial has a sapphire crystal that is slightly green at an angle, as you can see from the image gallery on their site. from.http://www.watchreport.com/2007/05/index.html