Page 58 of the Dresden Codex contains in its right-most columns (Figure 1) the heading of a computational table that follows the manuscript’s noted eclipse tables. The nature of the table on pages 58-59 is complex and subject to some debate, and here I will happily put aside any in-depth discussion of its numerology in order to simply point out an unusual paleographical feature of a day sign (13 Muluk) written in the page’s final column.
The numbers shown provide anchors or base dates for the calculations that follow on page 59, many of which are multiples of 780 days that fall on the day 13 Muluk. For example, we see in the first column two integrated Ring Numbers (RN), 1.7.11 and, added in red, 12.11. These calculate the intervals backwards before 13.0.0.0.0 to the intended base dates:
RN Base 1: 12.19.18.10.9 13 Muluk 2 Sak
RN Base 2: 12.19.19.5.9 13 Muluk 17 Tzek
13 Muluk 2 Sak is the primary of the two dates. It is recorded as the header of the two glyph columns on page 58 and as the CR at the lower right of the page, next to 4 Ahaw 8 Kumk’u.
The two intervals given on the right coloumn are so-called Long Reckonings, or a special type of Distance Number from the pre-era base date to reach a new base for the table. The first of these numbers is 9.18.2.2.0, which when added to the 12.19.18.10.9 13 Muluk 2 Sak results in 9.18.0.12.9 13 Muluk 2 Mol. The other LR record below it is 9.12.11.11.0 can also be added to the secondary base date (13 Muluk 17 Tzek), thereby reaching 9.12.10.16.9 13 Muluk 2 Sip. There is a bit of ambiguity in what gets added to what here, but the important point to stress here is that adding these LRs to either pre-era base date will always result in a 13 Muluk.
The day shown between the two LR numbers is obviously a Muluk, but different from others by two unusual features: it lacks a number coefficient and is surrounded by a red edging around the conventional black border (not shown in the Villacorta tracing, as it happens). Perusing the Dresden, I can find no other day sign with similar marking, even though red cartouches were common for painted day signs throughout the Classic period, and as far early as the Late Preclassic. No such red borders were ever used in the Dresden, however, and in light of the scribal style and practice employed in the Dresden I doubt that this red border is meant to be a decorative or without meaning.
The absence of the number prefix leads me to suspect that the red line around the Muluk is an unusual and playful means of indicating a 13 day coefficient — the fullest number possible that can accompany Muluk or any day sign in the 260-day tzolk’in. Perhaps the idea was that the number 13 has in some sense “come full circle.” It might be worth recalling that all number coefficients on tzolk’in dates are painted in red as well.
Admittedly this interpretation hinges on the assumption of highly unconventional scribal practice. But there are other examples of “odd” numbers in the Dresden. For example, phonetic spellings of the numbers three (ox, o-xo) and eleven (buluk, bu-lu-ku) with day signs in the Dresden are also well outside of normal conventions, never seen elsewhere. I’ll therefore put forward this idea of the circular 13 as a tentative hunch, hoping it explains the “missing” number on the day sign.