The second side of the Codex has to be treated in four divisions or chapters, the first of which includes pages 15 to 18. For numerical reasons which will appear, this chapter must probably have begun, however, at least one page further to the left.
These four pages are laid out with three main divisions, upper, middle and lower. Too much of the upper section is erased for any comment other than that its arrangement seems to have been parallel in all respects with the middle section. This latter shows three subsections, the backgrounds in some cases being red,[24-*] containing each a picture (probably of a god or a human figure in every instance), surmounted by a black and a red numeral and by six glyphs, in double column. This gives 12 subsections for the four pages, which we may refer to respectively as 15-_a_, _b_, _c_, etc. Of the initial pairs of glyphs in each subsection many are complete, and no section is left without the correct traces of the corresponding glyph for one or other of the positions; so that although 5 of the 24 glyphs are totally erased, we may safely restore them all. Other features of the comparative use and frequency of the glyphs on these pages have already been given.
At the top of each picture is found a black and a red numeral. These form the consecutive black "counters" or interval numbers, and the corresponding red day numbers of subdivided tonalamatls, so common in Dres. and Tro.-Cort. It is customary to find these tonalamatls divided into fifths or fourths, 52 or 65 days respectively--four or five trecenas. At the 53rd or 66th day the initial red number is again reached, and the calculation is (by hypothesis) repeated, starting again at the left with a new day-sign below the first. Such a column is seen in the lower part of page 17, where we find 6 Oc, Ik, Ix; these are to be completed by restoring below an erased Cimi and Ezanab, completing the 260 days and bringing us around again to 6 Oc. The total of all the black "counters" in any series must always be some multiple of 13, usually 52 or 65, as stated. And since each "counter" is the interval between its adjoining red numbers, wherever a red and a black number are given, the other red number, whether before or after, can always be filled in.