Where does Mark 1.1 come from and what does it mean?

There may be simply several sources for Mark 1.1. I tend to think it comes directly from the Priene Calendar


In the mail from @KregelAcademic: “A Commentary on the Manuscripts and Text of the New Testament “

By the way, this is the same size as the NA28 from Hendrickson… almost as if they meant it that