Somnus Explained · Issue Nº 04
Trust
in the
Number.
A score is only useful if it means the same thing every time.
Editor's Note: This is installment Nº 04 of Somnus Explained, a series on who we are, what we build, and the principles that guide the work. The principles themselves are set out in How We Work. This series expands on them.
Most sleep scores ask for trust and give little back. A number appears in the morning. It moves. Nobody says why.
Trust in a number comes from being able to see where it came from. So we build the Somnus Index to be honest by construction.
Why it matters
A number you cannot explain is a number you should not trust. If the same night could score two ways, neither score means much. If a score appears on a night the phone could not hear, it is a guess dressed up as a reading.
The Index is a wellness number you read against yourself. Its value is in the trend: this week against last, night 30 against night 1. A trend only works if every point in it was made the same way.
Why it is hard
Nights are messy. A fan hums. A partner talks. Some nights are almost silent. A score that insists on answering every night will be wrong on exactly those nights.
It is also tempting to keep tuning. A small change can make one night look better and quietly shift every night behind it. Software that changes without discipline drifts away from itself.
How we think about it
Same night, same number
The score locks when the night ends. Your history stays the history you saw.
No clear night, no number
If the phone could not hear the night well, you get no score instead of a guess. “Not enough to score” is an honest answer.
Reasons shown
Every score comes with what shaped it. You should be able to see why it moved.
You against you
The Somnus Index is built on your own baseline, never a population average. Every night adds to that baseline. Night 30 says more than night 1.
How it works
- Tested, then locked. The engine was tested against 60 held-out sleep-lab recordings, then locked.
- Replayed every release. Every release is replayed against the same set. If a number moves that should not, the release does not ship.
- Checked by rules. A learned model listens. Fixed rules check it. The rules can take a call away. They never add one.
- Plain bands. The Index runs 0 to 100. 85 to 100 is Strong. 70 to 84 is Steady. Under 70 is Building.
Across the beta so far: 1,100+ nights, 8,100+ hours, scored on the phone.
Nightsong is a wellness app. It does not diagnose, screen for, or treat any condition.
Questions we ask
- Would the same night score the same way twice?
- Did the phone hear enough to score, or would we be guessing?
- Can a person see why the number moved?
- Did anything move that should not? If it did, the change does not ship.
In short
Same night, same number. No clear night, no number. Reasons shown with every score. Tested against 60 held-out sleep-lab recordings, then locked, and replayed on every release. You against you.
What comes next
None of this holds because we wrote it down. It holds because it is built into the software. In installment Nº 05, we explain how a small team engineers privacy and values into the code instead of a binder.
We are glad to talk further about how we think and how we build. Reach us at [email protected].