In one sentence
The score your ring or watch gave last night, kept with the maker's name and the scale it uses; with Oura or Polar as your sleep source, it is the score VT shows for the night.
Why it is shown
Because you are used to it, and because a number you have watched for a year has value as a series even when its recipe is unknown. Every maker builds its score from a different mix of duration, stages, timing, heart rate and movement, weighted by rules it does not publish and changes without notice, so a 78 from one maker is not a 78 from another, and a 78 from the same maker may not be last year's 78.
Why VT does not score it, or score like it
Two reasons from the evidence. No study has shown a composite sleep score to discriminate health outcomes better than its best single component; of seven sleep domains tested against mortality in one older cohort, only regularity and continuity held up. And a score that leans on sleep stages leans on the least reliable figure a wearable produces (see Deep and REM sleep). There is also a cost to the number itself: sleep clinicians have described patients whose pursuit of a perfect tracker score became a cause of poor sleep, a pattern they named orthosomnia, which VT's own science article on optimal sleep discusses with its sources. VT's own scores lean on duration, regularity and continuity for that reason, and on nothing it cannot explain.
How Vitality Tracker uses it
Stored as the device's score with the device name and its valid range. With Oura or Polar as your sleep source, VT shows their nightly score; it scores the night itself only when they have not, or after you correct your sleep times, and it says so. The night's score, theirs or VT's, also nudges the sleep part of the Vitality Score's lifestyle area, by a factor between 0.85 and 1.05; nothing else uses it.
How far to trust the number
Estimate, of unknown recipe. As a trend on one device it tells you what that maker's model thinks changed; as a level it tells you nothing you can compare.
Sources
- Vitality Tracker Sleep Scoring Methodology, open specification v2.0.1, public edition (§1 design principles; §9.2 what this score is not).
- Vitality Tracker, Optimal sleep: what the evidence supports, and what it does not (Science, 8 October 2026), which carries the composite-score and orthosomnia discussion with its primary references, including Baron KG, et al. Orthosomnia: are some patients taking the quantified self too far? J Clin Sleep Med 2017;13:351–4. doi:10.5281/zenodo.23223863.