Wearable metrics capture activity and recovery data that inform daily plans. See Personalized Metrics for details. For how Apple Watch activity data becomes daily calorie and macro targets inside Fuel, see Apple Watch-Based Calorie Targets.
01Metric glossary and error margins
| Metric | What it tracks | Typical device error | Reliability rating |
|---|
| Steps and movement | NEAT and low-intensity output | +/- 5–15% | Medium |
| Heart rate (optical) | Cardio load and intensity | +/- 5 bpm at rest, wider during motion | Medium to high for intervals |
| Heart rate (chest strap) | Cardio load and intensity | +/- 1–2 bpm | High. Preferred for training decisions |
| Sleep duration and efficiency | Sleep quantity and continuity | Overestimates by 15–30 minutes | Medium. Depends on device |
| HRV | Readiness and nervous-system trends | High day-to-day variance | Medium. Strongest as 7+ day trend |
| Calorie burn estimate | Total daily energy expenditure | 30–50% error is typical | Low. Use as directional only |
02Confidence bands and interpretation
| Pattern | Band rule |
|---|
| Single-night drops | Treat as noise unless repeated 2 to 3 nights |
| Sudden spikes | Verify manually for context (illness, heat, stress) |
| Stable 2-week pattern | Use for plan-level decisions |
| Cross-device mismatch | Prefer manual baseline until one device repeats trend |
03Calibration workflow
Establish reliable baselines before acting on wearable data.
| Step | Action |
|---|
| 1 | Keep one device and one metric set for baseline period |
| 2 | Run 3 to 5 days of manual checks for sleep and steps |
| 3 | Compare trend direction before macro or calorie changes |
| 4 | Recalibrate if two metrics conflict for 7 to 10 days |
