Your ring gives you a “readiness” score. Here’s what’s inside it.
Wearables like Oura, Whoop and Apple Watch compress a night of sensor data into one friendly number. That’s useful — and it hides real signals worth understanding. Explore each metric on the 3D wrist below, and see how they combine into readiness.
Drag to rotate · sensor pulse follows your heart-rate slider
Readiness score
A weighted blend of resting HR, HRV, sleep and body temperature versus your own baseline. It answers one question: how hard can you push today?
The four signals that matter
Resting heart rate (RHR) is measured optically: a green LED shines into your skin and a photodiode reads how much light the pulsing blood absorbs (photoplethysmography, or PPG). A falling multi-week RHR usually signals improving fitness; a sudden spike often precedes illness or follows alcohol or poor sleep.
Heart-rate variability (HRV) is the millisecond variation between beats — counterintuitively, more variability is better. High HRV reflects a relaxed, parasympathetic “rest-and-digest” state; it collapses under stress, illness, and overtraining. HRV is deeply personal, so only compare it to your own baseline, never to a friend’s.
Sleep staging estimates light, deep, and REM sleep from movement, heart rate, and HRV patterns — good for trends, not clinical-grade (only a lab sleep study measures brain waves directly). Body temperature deviations flag illness, and for menstruating users can track cycle phase.
Wearables + AI: from data to action
The tweet’s point is the interesting one: raw wearable data becomes useful when something acts on it. Many devices (Oura, Whoop, Fitbit) expose developer APIs that return richer, higher-resolution data than the polished app shows — so you can build your own dashboards, or let an assistant read the context and do something: suggest a lighter workout on a low-readiness morning, nudge an earlier bedtime, or flag a multi-day RHR climb.
Two cautions. First, these are wellness devices, not diagnostic instruments — a scary number is a prompt to see a clinician, not a diagnosis. Second, this is among your most intimate data (sleep, stress, cycle, illness): before piping it into third-party tools, check who stores it, whether it’s sold, and whether you can delete it.