"Will I have my period the week of the wedding?" is a core prediction
question the app could not answer. The calendar marked only the next
forecast window and stopped browsing one month out, so a textbook-regular
user paged forward into blank months.
CycleProjection reaches a year. It is a separate type from Prediction,
deliberately: a forecast is something the app scores itself on -- the
period arrives inside the window or it does not, and PredictionRecord
writes down which -- while a projection eleven cycles out is never
scored, never learned from, and will have been replaced four times before
its date arrives. Separate types mean a projection cannot reach the
accuracy figures by accident.
Three rules keep it honest, each with a test named after it.
Uncertainty grows as sqrt(n), because cycle lengths are near-independent
draws: eleven cycles out is about three times as uncertain as one, not
eleven times. Real cycles do correlate, so that is the optimistic edge --
which is the second reason the assumption sentence is mandatory.
It declines rather than stretching. Past ten days either side a
projection stops being an answer, so the projection ends and reports that
it ended -- FertilityEstimate's precedent, which already refuses to show
a seventeen-day fertile window. The caller can tell "no period due here"
from "cannot see this far", and only the second invites her to log more.
The assumption is stated, not implied. Any month showing projected marks
carries "If your cycles continue as they have, this is the forecast" with
the confidence for that distance beside it. A year-ahead date drawn
without that is the clearest overstatement this app could make.
Cycle 1 is the engine's own forecast copied through unchanged, so the
calendar and the Today screen cannot disagree about the next period. The
typical cycle length comes from her own history and never a population
default -- projecting 29 days for a 35-day user is §3's core defect
repeated twelve times over.
PROJECTED_PERIOD is its own mark: the same dashed ring as a prediction,
thinner and finer. The family resemblance is the message -- still a
period, weaker claim -- and it survives greyscale, which an opacity
difference would not. Screen readers get the distance in the label, since
they cannot see that a square is months away.
Browsing now reaches a year; logging still stops at today.
ConfidenceRow and readable() move to feature/common and are shared with
the Today screen rather than copied. Two of them drifting apart is a
screen saying Medium in dots and Low in words.
closes#57
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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