With Rolex Watch U.S.A., Inc. service confirmation letter dated 29 March 2003.
1963 , The first Cosmograph, ref. 6239, is released this year with the very first serial numbers probably starting around 922,900.
The Cosmograph is powered by the 72 Valjoux-based calibre 72B movement, running at 18.000 beats per hour. It is equipped with a Microstella adjustable-inertia balance, featuring the Breguet overcoil spring, the Kif shock absorber unit, and a numbered main plate.
For the first time, the tachymeter scale is moved from the dial to the bezel. Early rare examples featured a particular scale, today known as the 'first series bezel with the 275 intermediate'.
The dial, produced by Singer, features two variants: black and silver grené, incorporating contrasting subsidiary registers. The very early dials produced are distinguished by applied glued indexes, and the reverse side of these carried the 'Singer Brevets AV' punch.
Furthermore, early examples show two Swiss designations, because Rolex originally used tools engineered for the previous chronograph models. The new large Daytona bezel now covers the outer SWISS designation, requiring another inner one.
Last but not least, extremely early 6239 display case backs engraved "6238", belonging to the previous chronograph model (today also known as the Pre-Daytona), used by Rolex while waiting for the correct ones to be delivered to the factory.
This specific 6239 presents a further particularity: the presence of a short straight tract just below the ROLEX COSMOGRAPH designation. It looks like a low underline to the designations (thus the "6239 underlined" nickname used among the collectors community). While Rolex never confirmed this, scholars agree it means that the radioactive radium previously used for the luminous indexes has been substituted with an alternative material compliant with the then-current regulations. The sub-registers have taken on a wonderful chocolate tone, which dramatically increases the charisma of this watch. The aesthetic appeal of such a configuration combined with the extreme rarity of underlined dials, used by Rolex for a very short time, makes this watch one of the rarest and most sought after early Cosmographs produced.