Sleep
How much sleep you need, what your tracker’s stages and scores can tell you, and what helps you sleep better.
Why a drink helps you fall asleep and then disrupts the second half of the night, what it does to REM sleep and heart rate, how much it takes, and how to see the effect in your own data.
November 4, 2026 · 2 min read
What a trial of caffeine 0, 3, and 6 hours before bed found, the meta-analysis behind the 8.8-hour rule for coffee, why sensitivity varies, and how to test your own cut-off.
November 4, 2026 · 3 min read
What a trial of 5-, 10-, 20-, and 30-minute naps found, why longer naps leave you groggy, the best time of day to nap, and how naps count towards your sleep.
November 4, 2026 · 2 min read
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
The AASM's 7 hours or more and the National Sleep Foundation's 7 to 9, what short and long sleep are linked to, why time in bed isn't time asleep, and how to judge your own sleep.
November 4, 2026 · 3 min read
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
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
How sleep studies count pauses in breathing, the 5, 15, and 30 thresholds for mild, moderate, and severe sleep apnea, why a home test's index reads lower, and what a watch can and can't tell you.
November 4, 2026 · 3 min read
How to rate how sleepy you feel right now on the 9-point scale, what research shows a score above 6 means for attention and driving, and how to use it to see what drives your sleepiness.
November 4, 2026 · 3 min read
What sleep efficiency, sleep onset latency, and wake after sleep onset measure, the values a National Sleep Foundation panel judged to mean good sleep, and what to do when yours fall short.
November 4, 2026 · 3 min read
Sleeping at the same times each day is its own part of good sleep. Here's how researchers measure it, what large studies have found, and how to follow your own.
November 2, 2026 · 4 min read
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