# What is the byte layout, scaling and checksum of a FreeD D1 packet, and where do public sources disagree?

- id: art_01M5MZ1WX6V601Z94RT7ADN2ZT
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T02, T19 · tags: none
- updated: 2026-10-23T18:06:01.119Z
- url: https://veyrul.com/articles/art_01M5MZ1WX6V601Z94RT7ADN2ZT

The stvmyr/freeD Go implementation (722d3054) and Vizrt Tracking Hub 1.7 docs both describe the 0x40-minus-byte-sum checksum over a 29-byte D1 packet; the Go code slices eight 3-byte fields at offsets 2-26.

The stvmyr/freeD Go implementation (722d3054) and Vizrt Tracking Hub 1.7 docs both describe the 0x40-minus-byte-sum checksum over a 29-byte D1 packet; the Go code slices eight 3-byte fields at offsets 2-26.

Curator qualifications: Correct 'two independent public descriptions': the Go readme points readers to a Vinten document and both may derive from the same BBC/Vinten specification; independence is not established. Axis labelling conflict (Go struct names vs readme table vs Vizrt example offsets) preserved as offered; no authoritative mapping read (Vinten/BBC primary unread). Rotation/position scaling (1/32768, 1/64) is code inference from one implementation. Static reading only; no tracker, camera, receiver or player connected or run.

Limitations: Static reading only; no tracker, camera, receiver or player connected or run.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://documentation.vizrt.com/tracking-hub-guide/1.7/Description_of_the_FreeD_Protocol.html",
      "note": "freeD.go Decode lines 19-34, checksum 85-93; readme lines 5-8, 46, 61; Tracking Hub 1.7 checksum element"
    },
    {
      "url": "https://factoryoptic.netlify.app/docs/networkinterface/freed/",
      "note": "freeD.go Decode lines 19-34, checksum 85-93; readme lines 5-8, 46, 61; Tracking Hub 1.7 checksum element"
    },
    {
      "url": "https://github.com/stvmyr/freeD/blob/722d305454a77160b0306cb336ef6df0f13e24b1/freeD.go",
      "note": "freeD.go Decode lines 19-34, checksum 85-93; readme lines 5-8, 46, 61; Tracking Hub 1.7 checksum element"
    },
    {
      "url": "https://github.com/stvmyr/freeD/blob/722d305454a77160b0306cb336ef6df0f13e24b1/readme.md",
      "note": "freeD.go Decode lines 19-34, checksum 85-93; readme lines 5-8, 46, 61; Tracking Hub 1.7 checksum element"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] The stvmyr/freeD Go implementation (722d3054) and Vizrt Tracking Hub 1.7 docs both describe the 0x40-minus-byte-sum checksum over a 29-byte D1 packet; the Go code slices eight 3-byte fields at offsets 2-26. · locator: freeD.go Decode lines 19-34, checksum 85-93; readme lines 5-8, 46, 61; Tracking Hub 1.7 checksum element · source: https://documentation.vizrt.com/tracking-hub-guide/1.7/Description_of_the_FreeD_Protocol.html

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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