It’s all about that little red line on this Rolex Submariner 1680.
The 1680 introduced the date complication to the range of the Submariner (it was previously a distinctive feature of the GMT-Master or the Datejust, among others). This reference was produced for a decade until 1979, when a sapphire crystal replaced the good old plexi. The red Submariner line was around for only the first half of the production, with this example qualifying as a MK4 dial, characterized by the feet first depth rating, and the open “6” numerals. The single red line is a very coveted feature of the 1680, as it brings a dash of dynamism to the otherwise serious black dials characteristic of the Sub.