Shared days
The days you share with someone, no verdicts
No sixteenth-century source compared two people's signs to judge whether they would get on. The whole corpus of Sahagún was searched, both volumes, and it does not appear once.
What they did do is documented, and it is another thing: choosing the day. For a marriage they sought a well-fortuned day, of a well-conditioned sign, and Sahagún names the ones that served — Acatl, Ozomatli, Cipactli, Cuauhtli, Calli.
That is where this feature's design comes from. The app does what the tradition did, choose the day, and not what it did not do, judge the couple. It shows you the days you share with someone: the ones that fall well for both. No verdicts and no percentages, because the sources give none and none are invented here.
Other people's dates are kept with an alias, never a name, and only if you confirm you have their permission.
Questions that reach this page
Is there compatibility between Aztec signs?
Not as there is in the Western zodiac. The whole corpus of Sahagún was searched and there is not one mention of comparing two people's signs. What the sources do document is choosing a favourable day for what two people undertake together, which is another thing, and it is what this app does.
Which Aztec signs are compatible?
The question has no answer in the sources, and any Aztec compatibility table you find is a modern invention. What can be said of two people is which days fall well for both, because that comes from the calendar and not from a judgement about them.