How this gets measured
What a ring or watch can actually know, what reaches Nila from which device, and the arithmetic behind every line we write. Published, because a disclaimer buried in the docs isn't disclosure.
Most wellness hardware sells you a single number. Readiness. Recovery. A sleep score out of a hundred. It feels like knowledge, and it's the part with the least evidence under it — a proprietary formula, on an estimate, from a sensor on your wrist.
Nila won't do it. We put your own entries beside your own device numbers on the same dates, describe where today sat in your own range, and stop. That decision only means something if we're willing to show our work, so here it is.
This is every step Nila takes between a number arriving and a sentence appearing on your day.
Nila needs at least five of your own days for a metric before it will say anything about it. There is no population baseline, no age band, no cohort you get placed against.
For each metric, your own recent values are sorted. Today lands in the bottom third, the middle, or the top third of your own range. That's the whole calculation — a percentile position, not a rating.
"Lower than most of your recent days" is a description of where a number fell. It isn't a verdict on the night, and it never becomes a readiness, recovery or sleep score.
No machine learning, no trained weights, no prediction. Sorting numbers and finding a third is arithmetic you could do on paper with the same data, and get our answer.
Where a device number and how you felt disagree, Nila treats how you felt as the more reliable of the two.
These are the studies that shaped the rule. They're worth reading if you're deciding how much to trust your own ring or watch.
Consumer sleep trackers vary widely against overnight sleep studies, and are weakest at exactly the thing they display most confidently: how long and how deeply you slept.
This is why Nila shows sleep hours as they arrived, and never builds a sleep score on top of them.
Read the sourceWrist optical sensors read heart rate less accurately on darker skin and during movement, because the measurement depends on light passing through tissue.
A number that is less accurate for some members must not be turned into a score that ranks them.
Read the sourceKeeping and appraising your own symptom record is associated with more help-seeking and better conversations with your doctor — the record itself is doing the work, before anyone interprets it.
This is why the daily check-in comes first and the device numbers come second.
Read the sourceApple Watch
via Apple Health, iPhone
The fullest picture of any device, because it writes straight into Apple Health.
iPhone alone, no watch
via Apple Health, iPhone
Your phone counts steps from your pocket. Sleep only appears if you use Apple's Sleep schedule or another app that writes it.
Oura ring
via Apple Health or Health Connect
Turn the sync on inside the Oura app first — Settings, then Apple Health or Health Connect.
Fitbit
via Google Health app, into Apple Health or Health Connect
HRV does not come through from Fitbit. The Google Health app (the renamed Fitbit app) cannot send it to either hub, so nothing on our side can pull it in.
Garmin
via Garmin Connect, into Apple Health or Health Connect
Garmin Connect has a per-category list of what it writes out. HRV depends on your model and on that list being switched on.
Samsung Galaxy Watch
via Health Connect, Android
Samsung Health writes into Health Connect once you allow it per data type.
Whoop
via Apple Health, partial Health Connect
Whoop shares less outward than the others and keeps its own scores inside its own app. Expect gaps.
Withings, Polar, Amazfit and most others
via Their own app, into Apple Health or Health Connect
Almost every tracker has an Apple Health or Health Connect switch buried in its settings. What comes through is whatever that app agrees to write.
Manual check-in, no device at all
via Nila, straight from you
You can run the whole of Nila without a wearable. Your own daily check-in is the part the research actually supports.
Checked against real synced data, September 2026.How this gets measured →
Nila never talks to your watch or ring directly. Everything arrives through Apple Health on iPhone or Health Connect on Android, so a blank column means the number never left your device's own app — not that you set something up wrong.
