The son jalisciense is the form the western dance repertoire is built on, and its bar is the reason people describe this music as running in two meters at once. That description is usually left as folklore. Here it is arithmetic.
The bar is written in 12 slots because 12 is the smallest grid on which both counts land on whole slots: three beats of four, and two beats of six. Slots 1, 5, 9 open the beats of the count in three; slots 1 and 7 open the beats of the count in six. Nothing about that is a choice — the engine derives both readings from the bar length’s own divisors.
Now look at where this cell puts its weight. Its accents sit on slots 1, 5, 7, 9 — exactly the union of the two readings’ downbeats and nothing else. Slot 7 carries weight that no waltz beat explains; slots 5 and 9 carry weight that no 6/8 beat explains. Both counts are therefore fully accented (3 of 3 and 2 of 2), both clear the carry threshold, and the bar genuinely answers to both. THAT disagreement is the thing the dance steps on.
The two slaps are not decoration either. They land on the second and third beats of the count in three, which is where a listener counting in three expects a chord and a listener counting in six does not — so the braked slot marks the argument between the counts without adding a pitch to it. Written as a bare alternation of down and up strokes, this bar would lose the entire fact.
DYNAMICS ARE NOT IN THE DATA, and deliberately so. The pattern stays the same from a whisper under a sung line to a full-ensemble drive; what changes is the weight in the arm. The cell says which slots get struck, not how hard, because how hard is the one thing that has to answer to the room.