Devices
How accurate your scale, watch, and other devices are, and what to do when they disagree.
Body
How bioelectrical impedance works, what a study of fifteen devices found, why hydration moves your reading, and how to weigh in so the trend means something.
November 4, 2026 · 3 min read
Location
Why a phone's position can be a few metres off outdoors and a hundred indoors, what the accuracy it reports means, and how that error shapes distance travelled, stays, and time at home.
November 4, 2026 · 4 min read
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
Sleep
What deep (slow-wave) and REM sleep do, roughly how much of a night each takes, what two large reviews say about change with age, and why chasing your watch's stage numbers can backfire.
November 4, 2026 · 3 min read
Vitals
What a peak flow meter measures, how to find your personal best, the green, yellow, and red zones of an asthma action plan, and how reliever use fits beside it.
November 4, 2026 · 3 min read
Air Quality
Why radon is a leading cause of lung cancer after smoking, the EPA's 4 pCi/L action level and the WHO's 100 Bq/m³ reference level, how to test, and why long-term averages matter more than one reading.
November 4, 2026 · 3 min read
Air Quality
What volatile organic compounds are and where they come from indoors, why a monitor's total VOC number has no health limit and is hard to compare, and why formaldehyde, the one VOC with clear guidelines, is the one worth measuring.
November 4, 2026 · 4 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
Sleep
How a CPAP machine estimates the breathing events left during treatment, why its number isn't a sleep study's, what high leak does to it, and how to read it alongside your hours of use.
November 4, 2026 · 3 min read
Air Quality
What fine particles are and why they harm health, the WHO's 5 µg/m³ annual and 15 µg/m³ daily guidelines, the EPA's 9.0 µg/m³ standard, and what indoor monitors can and can't tell you.
November 4, 2026 · 2 min read
Vitals
How fast each heartbeat's pressure wave travels, why stiffer arteries make it faster, the 10 m/s threshold in European guidelines, and how a bathroom scale estimates it.
November 4, 2026 · 3 min read
Vitals
The WHO's 95% to 100% range, when a low reading is an emergency, what makes oximeters read wrong, including skin pigmentation, and how to take a reading you can rely on.
November 4, 2026 · 3 min read
Vitals
A continuous glucose monitor measures the fluid under your skin, a meter measures blood. Why the two differ, especially when glucose is changing, how accurate each is allowed to be, and when to trust which.
November 4, 2026 · 3 min read
Fitness
A ten-second squeeze of a dynamometer is one of the simplest measures of overall strength. Here's what large studies link it to, and a standard way to measure it.
November 2, 2026 · 3 min read
Air Quality
What the guidelines actually say about carbon dioxide indoors, why 1,000 ppm comes up so often, and how to measure and follow the air in your own home.
October 27, 2026 · 5 min read
Two scales give two weights, and your phone and your watch count different steps. Here's why, which number to trust, and how to keep the comparison fair.
October 27, 2026 · 5 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 cuff, the arm, how you sit, and when you measure all change the number. Here's the method the American Heart Association recommends, step by step.
October 22, 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