diff --git a/docs/re/captures/arsenal-layout-validation.png b/docs/re/captures/arsenal-layout-validation.png
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diff --git a/docs/re/structures/ui-rat-layout.md b/docs/re/structures/ui-rat-layout.md
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--- a/docs/re/structures/ui-rat-layout.md
+++ b/docs/re/structures/ui-rat-layout.md
@@ -277,3 +277,40 @@ the running game:
   [movie table](../movie-subtitle-link.md) uses. A sub-component reads identically:
   `psselect_win1` declares 4 elements, three of them **parented to element 0**,
   which is the parent-index field doing real work on an independent pak.
+
+### Validated against the running game, to ±2 px
+
+The layout above is a static parse; this is the check that it predicts what the
+game actually draws. Booting to the ARSENAL and detecting the eight teal category
+chips by colour gives their row centres, against the eight `prbtn1…8.rat`
+placements from `eng\prmain_scr.prt`:
+
+```
+placement Y   + pivotY(14) + chrome(45)   observed centre   diff
+   166                225                      224          -1
+   220                279                      278          -1
+   276                335                      334          -1
+   331                390                      388          -2
+   385                444                      444          +0
+   441                500                      498          -2
+   496                555                      554          -1
+   551                610                      608          -2
+```
+
+The spacings are the real signature: **54, 56, 55, 54, 56, 55, 55** predicted
+against **54, 56, 54, 56, 54, 56, 54** observed — an irregular alternating pattern,
+not a round number that could match by luck. The single free parameter is the
+**45 px emulator window chrome** (title bar + menu bar), which is not part of the
+game; the ±2 px residual is the centroid measurement, since a thresholded chip
+centre is not exact.
+
+This confirms three things at once: the **declaration table is the element set**,
+the **placement region gives real screen coordinates**, and the **pivot composes
+additively** — `pivotY = 14` is half the 28 px chip, so placement is the top-left
+and pivot carries the centre offset, exactly as the record layout says.
+
+**Not** confirmed by this: the max-dwell rule for *animated* elements. These eight
+buttons are static (every keyframe identical), which is precisely why they make a
+clean ruler. Validating the animation rule needs an element captured mid-slide.
+
+Evidence: [`captures/arsenal-layout-validation.png`](../captures/arsenal-layout-validation.png).