Reference
Glossary
The words we use, defined the way we use them — including where a number is an estimate rather than a measurement.
| Readiness | A daily composite of resting heart rate, HRV, temperature deviation, respiratory rate and last night's sleep. Read the contributors, not the score. |
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| HRV | Heart-rate variability — the variation between consecutive heartbeats. Generally higher means better recovered, but the useful signal is your own baseline, not a population average. |
| SpO₂ | Estimated blood oxygen saturation. A consumer optical sensor gives a trend, not a clinical measurement. |
| Strain | Accumulated cardiovascular load for the day, derived from heart rate over time. |
| Sleep stages | Light, deep and REM bands inferred from movement, heart rate and HRV. An estimate with useful week-to-week trend value. |
| Electrochromic | A lens that darkens when a small voltage is applied. You control it, and it works behind a car windscreen. |
| Photochromic | A lens that darkens in response to UV. It handles itself, but does not react behind UV-filtering glass. |
| TAC | Laminated polarizing film. Light and inexpensive, used for sunglasses. |
| CR-39 | The standard optical plastic for prescription lenses. |
| IP68 | Dust tight and protected against continuous immersion in fresh water under test conditions. Not the same as a swimming rating. |