Trecena 15 runs from 1 Calli through 13 Cuauhtli, eagle, its span carrying house, lizard, serpent, death, deer, rabbit, water, dog, monkey, grass and reed before closing on the sign that opens Trecena 19 next in the round. This trecena sits within the count's final third, and its difficult reading under Itzpapalotl's patronage places it among the small number of trecenas the tonalpouhque treated as calling for the most active remedial attention, the shifting of naming days and the addition of penance the sources describe as standard responses to a harsh augury rather than exceptional measures reserved only for this week.
The eagle sign that closes this trecena carries, elsewhere in the count, a reading of solar vigour and warrior standing under its own patron Xipe Totec, a markedly different character from the house sign's enclosure at this trecena's opening, so that a reader working through these thirteen days in order would have narrated a movement from confinement toward the eagle's eventual flight, even within a week whose overall augury the sources record as unfavourable. Boone's study of the surviving books of fate notes that difficult trecenas like this one were not omitted or softened in the painted codices, a directness the Mexica calendar priesthood treated as essential to the count's usefulness.