diff --git a/.changeset/27994-fixed-currency-measure-refusals.md b/.changeset/27994-fixed-currency-measure-refusals.md
new file mode 100644
index 00000000000..e60a2495cc7
--- /dev/null
+++ b/.changeset/27994-fixed-currency-measure-refusals.md
@@ -0,0 +1,12 @@
+---
+'@objectstack/skills': patch
+---
+
+docs(skills): a dataset measure's `currency` no longer "always wins" over a `fixed` field; the skills teach the two `fixed` refusals
+
+Clause-②: no
+Metadata-protocol: none
+
+- `objectstack-data` `rules/field-types.md` (Currency resolution) and `objectstack-ui` `rules/dashboards.md` (the dataset currency comment) taught that a measure's own `currency` wins under `fixed`. Dataset compile now refuses, with `DATASET_INVALID` / 400, a measure `currency` that differs from its field's `fixed` code (delete it; restating the code is accepted) and a derived measure whose monetary operands resolve to two different `fixed` codes (derive from measures in one currency, or drop the operand in the other). Both files now say so, and keep the not-judged cases explicit: a `fixed` code against the tenant currency, and a measure `currency` over a `dynamic` field.
+- Paid for inside each file by deleting a restating code comment; the remainder raises the two token-ratchet rows on the standing path.
+- No schema, key or behaviour changes.
diff --git a/content/docs/api/data-api.mdx b/content/docs/api/data-api.mdx
index dfd4fcd4415..166c5247250 100644
--- a/content/docs/api/data-api.mdx
+++ b/content/docs/api/data-api.mdx
@@ -502,6 +502,14 @@ tenant default currency (the `localization.currency` setting), if one is set. A
 so its column shows the tenant default. The cube query on this page carries no column
 `currency`.
 
+Over a `fixed` field the measure's `currency` may only restate the field's code. A
+different code is refused when the dataset compiles, with `DATASET_INVALID` / 400: delete
+the measure's `currency`, and the column takes the field's code. A derived measure whose
+monetary operands resolve to two different `fixed` codes is refused the same way, whatever
+the operation: derive it from measures in one currency, or drop the operand in the other.
+Neither a `fixed` code against the tenant default nor a measure `currency` over a
+`dynamic` field is judged.
+
 A measure column over a `currencyMode: 'record'` amount has one currency per row, so it
 carries `currencyField` instead of `currency`: the name of the dimension column, in the same
 answer, that groups by the amount's code field (`currencyConfig.currencyField`). Each row's
diff --git a/content/docs/data-modeling/currency.mdx b/content/docs/data-modeling/currency.mdx
index ebd68eb13df..c09ce58a7a4 100644
--- a/content/docs/data-modeling/currency.mdx
+++ b/content/docs/data-modeling/currency.mdx
@@ -171,6 +171,18 @@ that column. A `count` column never carries `currencyField`. See the
   currency** (another code field, a `fixed` code, an explicit measure code or the tenant
   currency) is refused at compile with `DATASET_INVALID` / 400, whatever the operation.
   A derived measure over a `count`, such as an amount per invoice, stays legal.
+- **A dataset measure whose `currency` differs from its field's `fixed` code** is refused
+  at compile with `DATASET_INVALID` / 400: `currency: 'USD'` over a field fixed to `EUR`
+  would label euros as dollars. Delete the measure's `currency`, and the column takes the
+  field's code. A `currency` that restates the field's code is accepted.
+- **A derived measure whose monetary operands resolve to two different `fixed` codes** is
+  refused at compile with `DATASET_INVALID` / 400, whatever the operation. Derive it from
+  measures in one currency, or drop the operand in the other. A derived `sum` or
+  `difference` over one `fixed` code carries that code, so a measure built on it is judged
+  the same way.
+- **Not judged:** a `fixed` code against the tenant currency, which compile does not know,
+  and a measure `currency` over a `dynamic` field, which wins as the top of the currency
+  chain.
 
 ### In the Console
 
diff --git a/scripts/check-skills-token-ratchet.mjs b/scripts/check-skills-token-ratchet.mjs
index 289e5263252..829b116a619 100644
--- a/scripts/check-skills-token-ratchet.mjs
+++ b/scripts/check-skills-token-ratchet.mjs
@@ -679,7 +679,15 @@ export const CEILINGS = new Map([
   // zero headroom to absorb any of it, ceiling +126. Maintainer ruling
   // 2026-09-22 on decision batch #213 (item 1 carries the TOCs: 「四个超长 SKILL.md 按 500 行切,整段示例与 platform 的运维尾段下沉 references/,零删内容;同卡顺手:data 的 description 压到约 700 字符、长参考文件加目录」),
   // verbatim and untranslated: 「1 2 4 同意」.
-  ['skills/objectstack-data/rules/field-types.md', 3158],
+  // 3158 -> 3207 (#27994): the Currency resolution paragraph teaches the two `fixed`
+  // refusals #27991 added (a measure `currency` other than the field's `fixed` code; a
+  // derived measure over two `fixed` codes), each fix, and the not-judged tenant case.
+  // PAID DOWN FIRST by the Formula example's `returnType` comment, which restated the
+  // Calculated table's return types. The file is 12827 bytes -> 3207 tokens, zero
+  // headroom, ceiling +49, pinned AT the measurement. Standing ruling (2026-10-27, tap A,
+  // verbatim and untranslated): 「A:先削重复,余额按实测提高」; recognised path per ruling
+  // record 6513306068.
+  ['skills/objectstack-data/rules/field-types.md', 3207],
   ['skills/objectstack-data/rules/indexing.md', 3241],
   ['skills/objectstack-data/rules/lifecycle.md', 1590],
   ['skills/objectstack-data/rules/naming.md', 773],
@@ -827,7 +835,15 @@ export const CEILINGS = new Map([
   // follows it down to the new measurement, the ratchet's ordinary direction.
   // 6239 -> 6221 (#26602): LOWERED. The metric-widget bullet teaches the measure's `polarity`,
   // paid inside the file; the ceiling follows the file down to the measurement (24881 bytes).
-  ['skills/objectstack-ui/rules/dashboards.md', 6221],
+  // 6221 -> 6262 (#27994): the dataset currency comment teaches the two `fixed` refusals
+  // #27991 added, each fix, and the two not-judged cases. PAID DOWN FIRST: the metric
+  // example's `colorVariant` comment no longer restates that the measure's `format` /
+  // `currency` drive the number (Widget `options` says it), and the measure example in the
+  // currency comment shrinks to its `currency` key (the dataset above shows the shape).
+  // The file is 25047 bytes -> 6262 tokens, zero headroom, ceiling +41, pinned AT the
+  // measurement. Standing ruling (2026-10-27, tap A, verbatim and untranslated):
+  // 「A:先削重复,余额按实测提高」; recognised path per ruling record 6513306068.
+  ['skills/objectstack-ui/rules/dashboards.md', 6262],
   // 3011 -> 3141 (#19715, card item 4): a 5-line table of contents at the top,
   // anchors to the file's existing headings, nothing else changed. +132 tokens,
   // of which the row's 2 tokens of headroom absorb 2; the CEILING moves 130.
diff --git a/skills/objectstack-data/rules/field-types.md b/skills/objectstack-data/rules/field-types.md
index efef55ea9fb..019b2a657d4 100644
--- a/skills/objectstack-data/rules/field-types.md
+++ b/skills/objectstack-data/rules/field-types.md
@@ -181,8 +181,11 @@ Stored as JSON on the parent row — no separate table / FK:
 `{ value, currency }`. Shown: `'fixed'`, `defaultCurrency`; `'dynamic'`
 (default), the tenant `localization.currency`, else a plain number (never
 `$`); `'record'`, each record's code in the `text` field `currencyField`
-names (by convention `currency_code`), with `valueDomain: 'iso_4217_currency'`. Under
-`'fixed'`/`'dynamic'` a measure's own `currency` wins.
+names (by convention `currency_code`), with `valueDomain: 'iso_4217_currency'`. A
+dataset measure's own `currency` wins over a `'dynamic'` field; over a `'fixed'` one
+it may only restate the code, else `DATASET_INVALID` (delete it), as is a derived
+measure over two different `'fixed'` codes (derive from one currency or drop an
+operand). A `'fixed'` code is not judged against the tenant's.
 
 ### Select with Default
 
@@ -243,7 +246,7 @@ import { F } from '@objectstack/spec';
 const total = {
   type: 'formula',
   expression: F`record.amount * record.tax_rate`,
-  returnType: 'number',   // 'number' | 'text' | 'boolean' | 'date' | 'currency' (money; own currencyConfig)
+  returnType: 'number',   // see the Calculated table
 };
 ```
 
diff --git a/skills/objectstack-ui/rules/dashboards.md b/skills/objectstack-ui/rules/dashboards.md
index d12325d0fea..0e937873769 100644
--- a/skills/objectstack-ui/rules/dashboards.md
+++ b/skills/objectstack-ui/rules/dashboards.md
@@ -178,7 +178,7 @@ export const SalesDashboard: Dashboard = {
       dataset: 'opportunity_metrics', values: ['total_amount'],
       filter: { stage: { $nin: ['closed_won', 'closed_lost'] } },
       layout: { x: 0, y: 0, w: 3, h: 2 },
-      colorVariant: 'success',   // the accent; the measure's own `format` + `currency` drive the number
+      colorVariant: 'success',   // the accent only
       // Period-over-period: renderer fetches the prior quarter and
       // surfaces a secondary value + delta arrow automatically.
       compareTo: { kind: 'previousPeriod' },
@@ -295,13 +295,16 @@ defineDataset({
   dimensions: [{ name: 'signed_date', field: 'signed_date', type: 'date', dateGranularity: 'month' }],
   measures: [{ name: 'signed_count', aggregate: 'count' }],
 });
-// A money measure may set `currency` (ISO 4217):
-// `{ name: 'revenue', aggregate: 'sum', field: 'amount', currency: 'USD' }`.
+// A money measure may set `currency` (ISO 4217), e.g. `currency: 'USD'`.
 // Chain: measure `currency` → the field's `defaultCurrency` (`fixed`
 // only) → tenant `localization.currency`; omit it for counts. A
 // `currencyMode: 'record'` amount refuses `currency` and ungrouped
 // sum/avg/min/max; grouped by its code field, the column carries
-// `currencyField` (per-row code column); a `count` never does.
+// `currencyField` (per-row code column); a `count` never does. A `fixed`
+// field refuses a different `currency` (delete it; restating is fine), and
+// a derived measure refuses operands in two `fixed` codes (derive from one
+// currency or drop one). Not judged: `currency` over a `dynamic` field, a
+// `fixed` code against the tenant's.
 
 // The widget just selects the dimension by name:
 const signedByMonth: DashboardWidget = { id: 'signed_by_month', type: 'line',