Apple Health
What your iPhone and Apple Watch measure, how accurate they are, and how to bring their data together with the rest.
Fitness
How watches estimate VO₂ max from heart rate and pace, what validation studies found, why your estimate can be several points off, and how to get a trend worth following.
November 4, 2026 · 3 min read
Hearing
Why safe listening is a dose of loudness and time, the 85 dBA workplace limit and the WHO's 80 dB for 40 hours a week, how each 3 dB halves your safe time, and how to follow your exposure.
November 4, 2026 · 3 min read
Activity
The WHO's and the US guidelines' 150 to 300 minutes of moderate activity, how vigorous minutes count double, why any amount helps, and what a watch's exercise minutes do and don't count.
November 4, 2026 · 3 min read
Hearing
What the frequencies and decibels on a hearing test chart mean, how the pure-tone average is worked out, the WHO's grades of hearing loss, and how to compare tests over the years.
November 4, 2026 · 3 min read
Vitals
What a single-lead watch ECG records, what its classifications mean, what the Apple Heart Study found about irregular rhythm alerts, and why it can't detect a heart attack.
November 4, 2026 · 3 min read
Vitals
Why watches and rings report temperature as a change from your own baseline, what moves it, how it follows the menstrual cycle and illness, and why it isn't a thermometer.
November 4, 2026 · 3 min read
Vitals
For people with atrial fibrillation, the share of time spent in it. What the evidence links it to, how a watch estimates it, and what it can't tell you.
November 4, 2026 · 3 min read
A step-by-step guide to putting your iPhone's health data, your food diary, and your bank statements in one history, without counting anything twice.
October 27, 2026 · 4 min read
Sleep
What deep, light, and REM sleep really are, how a wearable estimates them, what studies against sleep lab recordings found, and which sleep numbers are worth tracking.
October 24, 2026 · 4 min read
Vitals
The 60 to 100 bpm range, why your own normal matters more than anyone's average, what moves resting heart rate up and down, and how to follow it over months.
October 21, 2026 · 5 min read
Vitals
What HRV measures, why SDNN and RMSSD give different numbers, and how to follow your own trend instead of comparing yourself with anyone else.
October 20, 2026 · 5 min read