Trecena 13 runs from 1 Ollin through 13 Atl, water, its span carrying movement, flint, rain, flower, crocodile, wind, house, lizard, serpent, death and deer before closing on the sign that opens Trecena 17 next in the round. This trecena sits just past the count's midpoint, and its opening day sign, carrying the same name as the present cosmic age, gave it a symbolic weight in Mexica thought that outran its ordinary place as merely the thirteenth of twenty trecenas, since Ollin's association with the fifth sun's eventual end by earthquake meant readers and clients alike approached this week aware of a cosmological resonance most trecenas did not carry.
The extremes of fortune the readers attached to this week's children mirror the movement sign's own reputation elsewhere in Mesoamerican calendrics as one of the most consequential and unpredictable of the twenty, a reputation this trecena's status as Tlazolteotl's week, governing confession and the clearing of the past, reinforces rather than softens. The thirteen numbered days within this span, read against their patron birds and against each day sign's own character, gave the tonalpouhque considerable room to distinguish a favourable from an unfavourable birth within what the trecena as a whole announced only as an extreme, fortune or ruin, rather than a single fixed outcome.