Maria's first data: the borrowed curve runs 35 minutes hot
2026-08-23
Maria's sleep journal went into the app today — 19 days of minute-precision logs, from two months old to two months and eighteen days.
Same routine as her brother: my partner and I write down every wake, every nap, every night waking, and sooner or later it becomes rows in a table. This batch went in through the same validation any hand-logged event has to pass. Within the hour, the habit layer had an opinion.
Her guidance runs on her brother's fitted pressure curve, because a borrowed curve is all a second child can possibly start with. So the first honest question was not does it work but how wrong is it, and in which direction. That is a question most products would rather not ask out loud about their own cold start.
Now I can answer it. Across fourteen comparable days, Maria falls asleep earlier than the borrowed curve predicts at every single nap position — about 45 minutes early for the first nap, then shrinking steadily through the day (37, 35, 33, 22, 12 minutes) — while her bedtime lands about 20 minutes later than predicted.
The satisfying part is that this is not noise, and it is not a bug. It is what the two-process model says should happen to a child whose sleep pressure builds faster than the prior assumes: shorter wake windows, all day long. And the corrections shrinking toward evening, then flipping late at bedtime, fits her age precisely — at two and a half months the circadian contribution is barely switched on, so the evening is expected to behave differently from the day. The prior was wrong in a shape the theory predicts. That is the best kind of wrong.
Two things I want on the record before anyone gets impressed:
- This is day one. Fourteen days of history feed those numbers, and the corrections will keep moving as she does. At this age the target changes faster than any average converges — I said so about newborns in another entry and I don't get to exempt my own child from it.
- Those corrections are per-child calibration wearing a different hat. The proper fix is fitting Maria her own pressure curve once there is enough data to fit one. Until then, the habit layer doing that job is the design working as intended, not a workaround quietly covering a hole. I'd rather name it than let it look like a feature.
The prediction league opened its first round for her today. In a few weeks there will be scored bets, and they will say which method copes best with a clock-emerging infant. The biology predicts the clock-time methods should struggle and the pressure-based ones should hold up.
That is a falsifiable claim, and it is on the record here before the data arrives. If it turns out backwards, this entry stays exactly where it is and I write the correction underneath.