Reference 6240 was the first "Oyster Cosmograph" model produced by Rolex. This novelty was predominantly characterized by the screw down push buttons. In production only during the second half of the 1960s, it was replaced by the better known references 6263 and 6265.
The present watch is distinguished by its early non-Oyster dial, not yet making reference to the screw down pushers. In fact, this example still features a dial version better known on reference 6239, for example, with the sought-after small, shifted Daytona designation. Only for a second generation of reference 6240, Rolex designed a dial with the Oyster denomination.
Another noteworthy fact is the designation "ROW" stamped on its movement, indicating that the original destination for the piece was the American market - and it is offered with two dials: its original silvered "non-Oyster" dial, and an additional later black ref. 6263 dial, at present mounted on the watch.
Other examples of Rolex chronograph models featuring the small "Daytona" designation are illustrated in 100 Superlative Rolex Watches by John Goldberger, p. 238, 246 & 247 and in Rolex Daytona - a legend is born by Carlo Pergola, Stefano Mazzariol, Giovanni Dosso, pp. 46 & 51.
Meanwhile, the more standard version of the reference 6240 with "Rolex Oyster Cosmograph dial" is described and illustrated in Rolex Daytona - A Legend is Born by Carlo Pergola, Stefano Mazzariol, Giovanni Dosso, pp. 76-92, in I Cronografi Rolex - La Leggenda by Pucci Papaleo Editore, pp. 304-311, and in 100 Superlative Rolex Watches by John Goldberger, p. 239.