What a composite hides
Average a fast-moving reading with a slow-moving one and you get a number that responds to neither. Tongue cleanliness can swing fifteen points overnight; brightness barely moves in a month. Blended, both become invisible.
Why five
- They move on different timescales — hours, days, weeks, months.
- They respond to different interventions, so only a separated reading tells you what to do.
- They fail independently. One low region against four steady ones is a signal; the same thing averaged is noise.
- They make the weekly focus possible. You can't target a composite.
So why does ToothPal still show a Smile Index?
Because people need somewhere to look. A composite is a legitimate navigational object — it tells you whether, broadly, things are going in a direction. It's a headline, not a finding.
The design rule is that the composite is never the only thing on screen, is always decomposable in one tap, and moves slowly enough that nobody mistakes it for a daily signal. It's deliberately damped.
And why Smile Age, then?
Fair question, since Smile Age is also a single number. The difference is honesty about its job: it exists to make the reading memorable and re-testable, not to be acted on. It shows its own breakdown on the same screen, it's labelled as a visual appearance index, and it's explicitly not a health measurement.
A number that admits what it is can be a good number. The problem was never composites — it was composites pretending to be findings.