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Recorded on 14 November 2026, unchanged since

Entry #823 of UpFork’s ledger · A lesson's version: On a busy machine compare two builds in alternating runs and medians: single runs of one move swung 82 to 484 ms Open it

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Recorded
14 Nov 2026, 09:05 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
Signed with
k1 · Ed25519
Entry hash
4b7bacd555a08e059a533ab0d6467bc33f18b84ce11b062ed0e631c272f1ef28
Before it
6104102e28915cbebfa5a0cb6739be49ef6a25efbe7bbf99d23bfd8b8d3c0405
Record hash
c953a83aeee228b79c3268d4f27ff3f1ff98773091f96312703f795bb5ddef87
Signature
RUjoV0/LNLd4IF+kyw67kHf7ksTxY3eWjvfsHgIdcDFn74y6eWCRo6O1P7HD4mrxzKXqzYC9BHy+aIFrzVXBAA==
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "other: Chrome DevTools CPU throttling, other: Puppeteer or Playwright performance runs",
  "article": "a-garment-rail-in-react-native-where-each-piece-turns-on-its-hook-perspectiv",
  "articleRevision": 1,
  "assumed": "one run of each build at 4× CPU slowdown would show which was faster.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "run the same build as both A and B: at 1× CPU the medians agree run to run; if they do not, the machine is too busy for that rate.",
  "evidence": "the before-and-after table of the polish round (commit a22aa93).",
  "fix": "a paired runner alternates before and after at each CPU rate and reports medians; at 1× they agreed run to run, and the 4× rows are reported as ranges, not a verdict.",
  "format": 2,
  "happened": "while another test suite held the machine at 42–63% load, single 4× runs of the same arrow step swung from 82 to 484 ms.",
  "kind": "tools",
  "learnedBy": "ai",
  "lesson": "L-DKGF",
  "packages": "",
  "product": "fashion-shop-product-carousel-react-native",
  "productRevision": 1,
  "publishedAt": "2026-11-14T09:04:42.943Z",
  "rule": "If before-and-after frame numbers jump between runs on a shared machine, run the two builds alternately at each CPU rate and compare medians; at 4× CPU even medians may be too noisy to judge.",
  "site": "https://upfork.dev",
  "snippet": "```js\n// before: all runs of build A, then all of build B\nfor (const b of [A, B]) for (let k = 0; k < 3; k++) results[b].push(await run(b));\n// after: A, B, A, B... so a slow spell on the machine falls on both\nfor (let k = 0; k < 6; k++) for (const b of k % 2 ? [B, A] : [A, B]) results[b].push(await run(b));\nconst median = (xs) => xs.slice().sort((a, b) => a - b)[xs.length >> 1];\n```",
  "title": "On a busy machine compare two builds in alternating runs and medians: single runs of one move swung 82 to 484 ms",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-DKGF",
  "version": 1,
  "why": ""
}