The present chronograph is an exceedingly rare example of the legendary Daytona model. Although Rolex were indeed producing chronographs since the 1930s, it wasn't until 1963 that this collection was grouped and named from its racing inspiration. The initial name, "Rolex Le Mans", was not popular and following Rolex’s arrival in the American market in 1964 it was decided to use “Daytona” instead, after the famous race held at Daytona Beach, Florida.
“Born” in 1963, these rare watches are also known as Mark 1. They launched the entire Daytona line, but noticeably do not have the "Daytona" designation on the dial which was only introduced the following year. Instead, we notice a small silver line below the signature “Cosmograph”. The meaning of this underline is not known but according to scholarship it could be to mark the new use of Tritium rather than Radium on the dials. Furthermore, the dial displays the designation "Swiss" twice, once in its usual placement below 6 o'clock, and again on the edge of the dial, (not fully visible while in the case). Hence, the nickname of this early model, "Underline Double Swiss". The counters on the dial also hold a particular variance. The running seconds hand is thinner with a flat head, whereas the hand for the chronograph are thicker with a pointed head.
In addition to the dial details, these early models display an unusual tachymeter scale on the bezel. The scale is calibrated to 300 units, instead of the more common 200 (which occurred later in approximately 1967), and in addition, the hash marks extend all the way round as opposed to only a portion of the way round the bezel. Finally, another highly notable quality of this example is the true sign of a Mark 1 Daytona, that the inside case back is stamped 6328, not 6239.
The present example is part of only a handful of such first series 6239 to appear in public to date. Preserved in very good, original overall condition it cannot but attract enormous interest among collectors.