The reference 6239 is Rolex’s first Cosmograph Daytona and marked their entry into the chronograph arena when it debuted in 1963, remaining in production until around 1969. Available in both stainless steel and yellow gold, this model introduced a groundbreaking tachymeter scale which is engraved on its bezel. Originally marketed as the "Le Mans", it earned its enduring name, the "Daytona", after Rolex became a sponsor of the 24 Hours of Daytona race. The present watch is a classic and well-preserved example of the reference 6239, proudly stamped "Daytona" above the subsidiary register at 6 o'clock.

What sets this watch apart from its peers is a small detail on the inside case back that may not be apparent to the casual observer. While one would typically expect to find "6239" or possibly "6238" stamped there, this particular watch bears the reference 6242. A brief search for this reference number yields few results, but investigative research reveals that these four digits are found on the inside caseback of the sole reference 6262 Yacht-Master prototype.

This suggests that Rolex initially intended to introduce reference 6242 into their production line, only to abandon the project later. It is even conceivable that this reference was meant for the elusive Yacht-Master line. Today, only a handful of these "prototype" watches are known to exist, one of which was previously owned by Eric Clapton. Having already produced these rare casebacks, Rolex chose to utilize the existing ones in their regular reference 6239 production line. Consequently, the present watch fortuitously features a 6242 case back, adding to its unique story and desirability.