The Milgauss model was designed for use in areas of high electro-magnetic fields, including laboratories and power stations. One of the most distinctive of all Rolex 'Sports' models, the 1019 was the last 'tool' watch - a watch designed for a specific activity. Despite being in production for over 20 years (1963-1985) it was never produced in significant numbers as demand was limited, thus making it very rare.
Further information on the Rolex Milgauss is discussed in The Best of Time - Rolex Wristwatches by James M. Dowling & Jeffrey P. Hess, p. 193. Examples of reference 1019 are illustrated in Vintage Rolex Sports Models by Martin Skeet & Nick Urul, pp. 95-96.