Field notes.

Occasional notes from the founder — short, plain-English reflections on what the data shows, what the math is doing, and what it's like to build Nightpenny solo. No marketing funnel. No newsletter form. If something here ages badly, the post stays up with a dated correction.

• May 26, 2026

  Can you actually catch up on sleep over the weekend?

  Short answer: partially. Recovery sleep helps, but not one-for-one — and not for everything sleep does. Here's what the research says and what it means for your week.

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• May 25, 2026

  Why Apple Health and your Apple Watch show different sleep numbers

  Apple Health, Apple Watch, and third-party sleep apps all measure something slightly different. Here's what each one actually counts, and why the gap is bigger than you think.

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• May 24, 2026

  Sleep debt vs sleep deprivation: what's the difference?

  Sleep debt is the running shortfall, accumulated over weeks. Sleep deprivation is the acute state — a short night, a missed night, a clinician's term. Here's how the two relate.

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