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Resolve the SBlk discrepancy: 40 is the record, markers are nested

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A fine scan settles it in favour of 40:

  stride 40  +0.454
  stride 39  +0.266
  stride 41  +0.215
  stride 38  +0.214

The peak is sharp and isolated, nearly twice its immediate neighbours, and
the multiples confirm it: 80 scores +0.376, 120 +0.394, 160 +0.340, while the
multiples of 12 (24, 48, 96, 144) all sit at 0.21 to 0.24.

So the record is 40 bytes and the 0x7f/0x47f markers at 12-byte spacing are a
nested structure inside those records, not the record boundary. Their spacing
is irregular -- 12, 24 and larger -- which is what one would expect of a field
present in some records and absent in others.

The previous commit's "they disagree" framing was itself wrong in one
respect: the marker spacing never claimed to be the record size. Read as a
claim about markers inside records rather than about the record itself, the
two measurements were never in conflict, and I had set up a false dichotomy
between them.
This commit is contained in:
ReaperOfVeriod
2026-10-11 04:06:42 +02:00
parent 5df3914160
commit 0f1a7f27c7
1 changed files with 25 additions and 4 deletions
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docs/formats/core-data-regions.md
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@@ -592,7 +592,28 @@ explaining the other. Recorded as an open discrepancy rather than resolved in
favour of either: the marker spacing says 12, the period says 40, and 40 being
twice as strong is the more surprising of the two.
This is the first place in this project where two sound measurements of the
same data point at incompatible answers. Worth resolving before any record
layout is attempted, because a layout built on the wrong one will parse
plausibly and be wrong.
### Resolved: 40 is the record, the 12-byte markers are nested
A fine scan settles it in favour of 40.
| stride | excess |
|---|---|
| **40** | **+0.454** |
| 39 | +0.266 |
| 41 | +0.215 |
| 38 | +0.214 |
The peak is sharp and isolated -- nearly twice its immediate neighbours.
And the multiples confirm it: 80 scores +0.376, 120 +0.394, 160 +0.340,
while the multiples of 12 (24, 48, 96, 144) all sit at 0.21-0.24.
So the record is **40 bytes**, and the `0x7f`/`0x47f` markers at 12-byte
spacing are a nested structure *inside* those records rather than the record
boundary. Their spacing is irregular -- 12, 24 and larger -- which is exactly
what one would expect of a field that is present in some records and absent in
others.
The earlier "they disagree" framing was wrong in one respect: the marker
spacing never claimed to be the record size. Read as a claim about markers
inside records rather than about the record itself, the two measurements were
never in conflict.