This is a rare Rolex Prince "Railway" watch. This model was given this name due to the fact that these cases resembled early railroad cars. This is a reference 1768 and dates to 1930. This watch is powered by a chronometer grade 18 jewel movement which is adjusted to 6 positions. Truly an amazing engineering feat based upon its age. 

The 9K yellow gold case measures 20mm x 35mm and is in very good condition. 

This is a rare Rolex model. A true collectors piece.