Reference 6240 was the first "Oyster Cosmograph" model produced by Rolex. This novelty predominantly was characterized by the screw down push buttons. Reference 6240 was only in production during the second half of the 1960s and was replaced by the better known references 6263 and 6265.
The present watch is a highly attractive example of this model, featuring a warm chocolate-brown "tropical" dial and retains all the elements demanding collectors expect from an early Oyster Cosmograph: the finely reeded screw down buttons (later generations were deeper carved for improved grip), no Daytona designation, the proper 6240 case back and calibre 722.
Reference 6240 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, Pucci Papaleo Editore, pp. 304-311, and in 100 Superlative Rolex Watches by John Goldberger, p. 239.