diff --git a/docs/plan/level-assets.md b/docs/plan/level-assets.md
index 826e5d6..41f80e5 100644
--- a/docs/plan/level-assets.md
+++ b/docs/plan/level-assets.md
@@ -1405,3 +1405,43 @@ checked yet.
 not be listed as unparsed geometry. What it contains *after* the descriptor is
 still unknown, and the file is large enough that the descriptor is unlikely to
 be all of it.
+
+## Tie spans: a constant first word, and three quantized floats
+
+**Range measured:** all **1,864 tie spans across 27 levels**, read at each
+class entry's geometry offset.
+
+**Method:** read `+0x00`, `+0x0c` and the three `f32` at `+0x10`, `+0x14`,
+`+0x18`, and count distinct values per position.
+
+**Result:**
+
+- `u32@+0x00` takes **exactly one value across all 1,864 spans** -- `0x00000100`,
+  256. A constant first word across the whole disc.
+- `+0x0c` takes **83 distinct values**, so it is not constant.
+- The three floats take **103 distinct triples** built from **42 distinct
+  values**, and those values are round: 4, 8, 9, 10, 12, 15, 16, 18, 20, 24,
+  25, 30 ... Only 10 of the 42 are exact powers of two.
+
+Two spans on level 0 open:
+
+    +000  00000100 00005070 000065c0 07050612
+    +010  41400000 41c80000 42200000 00009460
+
+and the same second, different first-two:
+
+    +000  00000100 00007ca0 0000a040 0605091e
+    +010  41400000 41c80000 42200000 0000ddf0
+
+**What this rules out.** The three floats are not a general bounding box: a box
+would take continuous values, and these come from a 42-value set of round
+numbers. They are authored or quantised quantities -- a grid, a size class, or a
+set of LOD thresholds -- and nothing measured here separates those.
+
+**Correction to an earlier reading.** These floats were previously read as a
+bounding-box minimum, from level 0's first two spans happening to share
+(12.0, 25.0, 40.0). That triple holds on 266 of 1,864 spans, not all of them,
+and the value set is quantised. The bounding-box reading does not survive.
+
+**Not decoded:** what the three floats are, what `0x100` at `+0x00` counts,
+and what the 83 values at `+0x0c` are.