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How an Atomic Clock Really Works: Inside the HP 5061A Cesium Clock

CuriousMarc · explainer · Watch on YouTube

Electronics & circuit designEveryday physics & science demosHistory of computing

What it is

CuriousMarc powers up a vintage HP 5061A cesium beam clock and explains both the quantum principle and the HP implementation in detail. It is part of a longer atomic clock series.

Why Hacker News recommends it

HN calls it one of the best explanations of how atomic clocks actually work.

  • 4 people recommended it
  • 4 different months
  • 2 strong recommendations
  • first 2020, last 2026

What HN commenters said

  1. “CuriousMarc has an excellent episode on an atomic clock.”

    Excellent atomic clock episode

    somat, 2022-10 · Strong recommendation · in “Time is an illusion, Unix time doubly so”

  2. “I've yet to see a description better than in CuriousMarc's HP 5061A series”

    Best description of how atomic clocks work

    alnwlsn, 2026-08 · Strong recommendation · in “Atomic Clocks”

  3. “It's interesting to see that atomic clocks aren't just some giant laboratory thing”

    Explains a vintage 1960s HP cesium atomic clock

    kens, 2020-03 · Recommendation · in “Living Without Atomic Clocks (2016)”

  4. “was really fascinating”

    Startup of cesium clock compared to GPS reference

    puzzledobserver, 2022-12 · Recommendation · in “The state of the art in amateur timekeeping (2003) [pdf]”

Excerpts from Hacker News comments, linked to the originals. Summaries and labels were written by a language model from those comments.

Topics: cesium clock, hp 5061a, timekeeping, vintage electronics, quantum physics

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