Patek Philippe first launched reference 591 in 1938. At the time of production, the model was entirely different from anything that the manufacture had ever produced. The case, produced by Wenger, featured "bean" shaped lugs, lovingly dubbed "Fagiolino", or "little bean". The angular, and relatively sharp lines starkly contrasted with the smooth Calatrava design of reference 130 and 533. Reference 591 was also larger than its chronograph siblings, boasting a 34 millimeter case diameter, giving the watch a modern aesthetic today.

This particular example is preserved in wonderful condition, with a crisp and sharp hallmark between the pushers. The dial furthermore retains its long signature, with a strong accent in the "Genève" text. Retaining its original crown, one can admire how remarkably well-preserved the lugs are. It is particularly easy to spot polishing on this reference, as the lugs and bezel easily lose their definition.

It is interesting to note that the inside case back has multiple service markings from the same watchmaker. One can only conclude that the watch was lovingly well preserved and maintained by its previous owner.

Reference 591 was produced in exceedingly small numbers. In fact, it is the rarest chronograph model that the firm produced throughout the 1930s and 1950s. Research suggests that less than 17 examples cased in yellow gold have appeared on the market thus far, with approximately 34 examples produced in total. The last yellow gold example surfaced in 2013, which really enhances the utmost rarity of the present watch.