• 01 / 08ms HRVHeart Rate VariabilityThe tiny changes in timing between your heartbeats.Tap to decode

  What it meansHRV

  Measured in milliseconds, usually while you sleep. A higher number than your own normal often points to good recovery.

  Good to knowIt is very personal. Compare it with your own baseline over weeks, not with someone else’s number.

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• 02 / 08bpm RHRResting Heart RateHow fast your heart beats when you are fully at rest.Tap to decode

  What it meansRHR

  Most wearables take it during sleep. Many adults sit somewhere between 60 and 100 bpm, and fit people often lower.

  Good to knowA jump of a few beats above your usual can follow a late meal, alcohol, stress, poor sleep or a cold coming on.

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• 03 / 08% SpO2Blood Oxygen SaturationHow much of your blood’s haemoglobin is carrying oxygen.Tap to decode

  What it meansSpO2

  Healthy readings are usually in the mid to high 90s. Rings and watches estimate with sensors that shine light through the skin.

  Good to knowWearable readings are wellness estimates, not a medical test. Talk to a doctor if you are worried about a reading.

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• 04 / 08ml/kg/min VO2 maxMaximal Oxygen UptakeThe most oxygen your body can use during hard exercise.Tap to decode

  What it meansVO2 max

  A well-known marker of cardio fitness. Watches estimate it from your heart rate and pace on runs, rides or walks.

  Good to knowTreat it as a trend line. Only a lab test with a mask on a treadmill or bike measures it directly.

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• 05 / 080–100 ReadinessReadiness and Recovery ScoresOne number that tries to say how ready you are today.Tap to decode

  What it meansReadiness

  Brands blend things like HRV, resting heart rate, sleep and temperature into a single daily score.

  Good to knowEvery brand mixes it differently, so an Oura score and a WHOOP score are not comparable with each other.

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• 06 / 08± °C Skin TempSkin Temperature TrendHow your skin temperature shifts from your own normal.Tap to decode

  What it meansSkin Temp

  Usually shown as a change from your baseline overnight, not as a body temperature like a thermometer gives.

  Good to knowShifts can line up with getting ill, travel, alcohol or the menstrual cycle, which is why smart ring brands use it for cycle insights.

  Read our stories243
• 07 / 08hrs Sleep StagesLight, Deep and REM SleepAn estimate of how your night splits into sleep stages.Tap to decode

  What it meansSleep Stages

  Wearables guess stages from your movement and heart rhythm. They are good at total sleep time and timing.

  Good to knowStage splits are estimates. A clinical sleep study in a lab (polysomnography) is the reference method.

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• 08 / 08mV ECGElectrocardiogramA short recording of your heart’s electrical signal.Tap to decode

  What it meansECG

  Some watches and rings can record a single-lead ECG and check for signs of atrial fibrillation (AFib).

  Good to knowIt cannot detect a heart attack. If you feel unwell, call your local emergency number rather than relying on a watch.

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General information only, not medical advice. Wearable readings are estimates; speak to a doctor about anything that worries you.