diff --git a/packages/instrument-utils/AGENTS.md b/packages/instrument-utils/AGENTS.md
index e8f38dcc0..01f3f90e4 100644
--- a/packages/instrument-utils/AGENTS.md
+++ b/packages/instrument-utils/AGENTS.md
@@ -18,8 +18,10 @@ handled. That coupling is the point — do not add a catch-all pattern to make i
 fails `$InstrumentMeasureValue`, or whose label cannot be resolved, is `console.error`ed and dropped
 from the returned record; non-object `data` returns `{}`. The visible symptom is a summary missing a
 row, not an error. Check a measure's `ref` and `label` rather than trusting that the page rendered.
-A `computed` measure is different: its author-supplied `value(data)` function is called bare, so if
-it throws, the whole computation throws.
+A `const` measure on a dynamic form field that the data keeps hidden (`isFieldHidden`) is dropped
+without a log, label or not: the respondent never saw that question. A `computed` measure is
+different: its author-supplied `value(data)` function is called bare, so if it throws, the whole
+computation throws.
 
 **`isScalarInstrument` tests `Object.hasOwn(instrument, 'internal')`, not `kind`.** See
 `.agents/docs/architecture/instrument-pipeline.md` for why.
@@ -29,6 +31,6 @@ appearing in two groups silently keeps the last one.
 
 ## Tests
 
-`pnpm exec vitest --project instrument-utils`. `src/__tests__/` covers `getFormFields`; everything
-else here is still covered only through its consumers' suites (`apps/api`, `apps/web`) and the
-Playwright suite in `testing/`.
+`pnpm exec vitest --project instrument-utils`. `src/__tests__/` holds one file per module. The
+results summary that `computeInstrumentMeasures` feeds is exercised end to end by
+`testing/src/specs/playground.spec.ts`.
diff --git a/packages/instrument-utils/src/__tests__/form.test.ts b/packages/instrument-utils/src/__tests__/form.test.ts
index 9eeb6dc73..6e83315d6 100644
--- a/packages/instrument-utils/src/__tests__/form.test.ts
+++ b/packages/instrument-utils/src/__tests__/form.test.ts
@@ -1,7 +1,7 @@
 import type { FormInstrument, Language } from '@opendatacapture/runtime-core';
 import { describe, expect, it } from 'vitest';
 
-import { extractFieldLabel, getFormFields } from '../form.js';
+import { extractFieldLabel, getFormFields, isFieldHidden } from '../form.js';
 
 type TData = { a: number; b: number };
 
@@ -65,3 +65,28 @@ describe('extractFieldLabel', () => {
     expect(extractFieldLabel<TData>(dynamicForm, 'a', { a: 1, b: 2 })).toBeUndefined();
   });
 });
+
+describe('isFieldHidden', () => {
+  const form = {
+    content: {
+      a: fieldA,
+      b: {
+        deps: ['a'],
+        kind: 'dynamic',
+        render: (data: { a?: number }) => (data.a ? { kind: 'number', label: 'B', variant: 'input' } : null)
+      }
+    }
+  } as unknown as FormInstrument<TData, Language>;
+
+  it('should report a dynamic field hidden while its render function returns null for the data', () => {
+    expect(isFieldHidden<TData>(form, 'b', {})).toBe(true);
+  });
+
+  it('should report a dynamic field shown once its render function returns a field for the data', () => {
+    expect(isFieldHidden<TData>(form, 'b', { a: 1 })).toBe(false);
+  });
+
+  it('should never report a static field hidden, since the respondent always sees it', () => {
+    expect(isFieldHidden<TData>(form, 'a', {})).toBe(false);
+  });
+});
diff --git a/packages/instrument-utils/src/__tests__/measures.test.ts b/packages/instrument-utils/src/__tests__/measures.test.ts
index ec1e4fa64..05199f34a 100644
--- a/packages/instrument-utils/src/__tests__/measures.test.ts
+++ b/packages/instrument-utils/src/__tests__/measures.test.ts
@@ -16,6 +16,28 @@ const formInstrument = {
   }
 } as unknown as AnyUnilingualScalarInstrument & { content: FormInstrument.Content<TData, Language> };
 
+type TDynamicData = { hasPet: boolean; petName?: string };
+
+const dynamicFormInstrument = {
+  content: {
+    hasPet: { kind: 'boolean', label: 'Has Pet', variant: 'radio' },
+    petName: {
+      deps: ['hasPet'],
+      kind: 'dynamic',
+      render: (data: FormInstrument.PartialData<TDynamicData>) => {
+        return data.hasPet ? { kind: 'string', label: 'Pet Name', variant: 'input' } : null;
+      }
+    }
+  },
+  internal: { edition: 1, name: 'STUB_DYNAMIC_FORM' },
+  kind: 'FORM',
+  language: 'en',
+  measures: {
+    labeledPetName: { kind: 'const', label: 'Name of Pet', ref: 'petName' },
+    petName: { kind: 'const', ref: 'petName' }
+  }
+} as unknown as AnyUnilingualScalarInstrument;
+
 const interactiveInstrument = {
   internal: { edition: 1, name: 'STUB_INTERACTIVE' },
   kind: 'INTERACTIVE',
@@ -47,6 +69,15 @@ describe('computeInstrumentMeasures', () => {
     expect(result.favoriteNumber).toEqual({ label: 'Favorite Number', value: 7 });
   });
 
+  it("should read a 'const' measure's value and label through its ref, so a measure keyed apart from its field still shows that field", () => {
+    const instrument = {
+      ...formInstrument,
+      measures: { favorite: { kind: 'const', ref: 'favoriteNumber' } }
+    } as unknown as AnyUnilingualScalarInstrument;
+    const result = computeInstrumentMeasures(instrument, { favoriteNumber: 7 });
+    expect(result.favorite).toEqual({ label: 'Favorite Number', value: 7 });
+  });
+
   it("should use a 'const' measure's own label when it declares one", () => {
     const instrument = {
       ...formInstrument,
@@ -71,4 +102,25 @@ describe('computeInstrumentMeasures', () => {
     expect(result.message).toBeUndefined();
     expect(console.error).toHaveBeenCalledOnce();
   });
+
+  it('should leave out a labeled measure on a dynamic field its data keeps hidden, since the respondent never saw it', () => {
+    const result = computeInstrumentMeasures(dynamicFormInstrument, { hasPet: false });
+    expect(result.labeledPetName).toBeUndefined();
+  });
+
+  it('should keep a labeled measure on a dynamic field once its data reveals it', () => {
+    const result = computeInstrumentMeasures(dynamicFormInstrument, { hasPet: true, petName: 'Rex' });
+    expect(result.labeledPetName).toEqual({ label: 'Name of Pet', value: 'Rex' });
+  });
+
+  it('should leave out an unlabeled measure on a hidden dynamic field without logging, since nothing failed', () => {
+    const result = computeInstrumentMeasures(dynamicFormInstrument, { hasPet: false });
+    expect(result.petName).toBeUndefined();
+    expect(console.error).not.toHaveBeenCalled();
+  });
+
+  it('should keep a measure on an unanswered static field, so the summary still shows it as missing', () => {
+    const result = computeInstrumentMeasures(formInstrument, {});
+    expect(result.favoriteNumber).toEqual({ label: 'Favorite Number', value: undefined });
+  });
 });
diff --git a/packages/instrument-utils/src/form.ts b/packages/instrument-utils/src/form.ts
index 507034633..827e3d430 100644
--- a/packages/instrument-utils/src/form.ts
+++ b/packages/instrument-utils/src/form.ts
@@ -15,6 +15,16 @@ export function getFormFields<TData extends FormInstrument.Data>(
   }, {}) as FormInstrument.Fields<TData, Language>;
 }
 
+/** Whether the field is a dynamic one that `data` keeps hidden, so the respondent never saw it */
+export function isFieldHidden<TData extends FormInstrument.Data>(
+  form: FormInstrument<TData, Language>,
+  key: string,
+  data: { [key: string]: unknown }
+) {
+  const field = getFormFields(form.content)[key];
+  return field?.kind === 'dynamic' && field.render(data as FormInstrument.PartialData<TData>) === null;
+}
+
 export function extractFieldLabel<TData extends FormInstrument.Data>(
   form: FormInstrument<TData, Language>,
   key: string,
diff --git a/packages/instrument-utils/src/measures.ts b/packages/instrument-utils/src/measures.ts
index adcbc14d4..7c18b3390 100644
--- a/packages/instrument-utils/src/measures.ts
+++ b/packages/instrument-utils/src/measures.ts
@@ -1,9 +1,14 @@
 import { isPlainObject } from '@douglasneuroinformatics/libjs';
-import type { AnyUnilingualScalarInstrument, InstrumentMeasureValue } from '@opendatacapture/runtime-core';
+import type {
+  AnyUnilingualScalarInstrument,
+  InstrumentMeasures,
+  InstrumentMeasureValue,
+  Language
+} from '@opendatacapture/runtime-core';
 import { $InstrumentMeasureValue } from '@opendatacapture/schemas/instrument';
 import { match } from 'ts-pattern';
 
-import { extractFieldLabel } from './form.js';
+import { extractFieldLabel, isFieldHidden } from './form.js';
 import { isFormInstrument } from './guards.js';
 
 export type ComputedMeasures = { [key: string]: { label: string; value: InstrumentMeasureValue } };
@@ -14,14 +19,19 @@ export function computeInstrumentMeasures(instrument: AnyUnilingualScalarInstrum
     console.error(`Cannot compute measures from data: ${JSON.stringify(data)} is not an object`);
     return computedMeasures;
   }
-  for (const key in instrument.measures) {
-    const result = match(instrument.measures[key]!)
+  // Widened because `data` is untyped: under an interactive instrument's `Json` data, `ConditionalKeys`
+  // makes `ref` a union of `Json[]` members (numbers, array methods), which cannot index `data`.
+  const measures: InstrumentMeasures<any, Language> | null = instrument.measures;
+  for (const key in measures) {
+    const result = match(measures[key]!)
       .with({ kind: 'computed' }, (measure) => {
-        // @ts-expect-error - this is ignored because it is safer than the previous (any) solution
         return { label: measure.label, value: measure.value(data) };
       })
       .with({ kind: 'const' }, (measure) => {
-        const result = $InstrumentMeasureValue.safeParse(data[key]);
+        if (isFormInstrument(instrument) && isFieldHidden(instrument, measure.ref, data)) {
+          return null;
+        }
+        const result = $InstrumentMeasureValue.safeParse(data[measure.ref]);
         if (!result.success) {
           console.error('Failed to Parse Constant Measure', result.error);
           return null;
@@ -32,10 +42,10 @@ export function computeInstrumentMeasures(instrument: AnyUnilingualScalarInstrum
           label = measure.label;
         } else if (isFormInstrument(instrument)) {
           // @ts-expect-error - this is ignored because it is safer than the previous (any) solution
-          label = extractFieldLabel(instrument, key, data);
+          label = extractFieldLabel(instrument, measure.ref, data);
         }
         if (!label) {
-          console.error(`Failed to extract label for key '${key}' from data '${JSON.stringify(data)}'`);
+          console.error(`Failed to extract label for key '${measure.ref}' from data '${JSON.stringify(data)}'`);
           return;
         }
         return { label, value: result.data };
diff --git a/packages/react-core/src/components/InstrumentSummary/__tests__/InstrumentSummary.test.tsx b/packages/react-core/src/components/InstrumentSummary/__tests__/InstrumentSummary.test.tsx
index bf093937f..b3f110203 100644
--- a/packages/react-core/src/components/InstrumentSummary/__tests__/InstrumentSummary.test.tsx
+++ b/packages/react-core/src/components/InstrumentSummary/__tests__/InstrumentSummary.test.tsx
@@ -7,6 +7,7 @@ import { afterEach, beforeAll, describe, expect, it, vi } from 'vitest';
 import { InstrumentSummary } from '../InstrumentSummary';
 
 const baseInstrument = {
+  content: {},
   details: { title: 'Stub Form' },
   internal: { edition: 1, name: 'STUB_FORM' },
   kind: 'FORM',
diff --git a/testing/src/specs/playground.spec.ts b/testing/src/specs/playground.spec.ts
index 2002a09a9..e12d111cc 100644
--- a/testing/src/specs/playground.spec.ts
+++ b/testing/src/specs/playground.spec.ts
@@ -61,6 +61,41 @@ export default defineInstrument({
 `;
 }
 
+/**
+ * A form that asks for a pet's name only once the respondent says they have a pet. Both questions
+ * carry a labeled measure, so the toggle's measure is always in the summary and the name's only when
+ * the question was shown.
+ */
+function dynamicMeasureInstrumentSource(title: string): string {
+  return `
+import { defineInstrument } from '/runtime/v1/@opendatacapture/runtime-core';
+import { z } from '/runtime/v1/zod@3.x';
+
+export default defineInstrument({
+  kind: 'FORM',
+  language: 'en',
+  tags: ['Measures'],
+  internal: { edition: 1, name: 'DYNAMIC_MEASURE' },
+  clientDetails: { estimatedDuration: 1, instructions: ['Submit the form'] },
+  content: {
+    hasPet: { kind: 'boolean', label: 'Has Pet', variant: 'radio' },
+    petName: {
+      kind: 'dynamic',
+      deps: ['hasPet'],
+      render: (data) => (data.hasPet ? { kind: 'string', label: 'Pet Name', variant: 'input' } : null)
+    }
+  },
+  defaultMeasureVisibility: 'visible',
+  details: { description: 'Dynamic field measure', license: 'Apache-2.0', title: '${title}' },
+  measures: {
+    hasPet: { kind: 'const', label: 'Has Pet Measure', ref: 'hasPet' },
+    petName: { kind: 'const', label: 'Pet Name Measure', ref: 'petName' }
+  },
+  validationSchema: z.object({ hasPet: z.boolean(), petName: z.string().optional() })
+});
+`;
+}
+
 // The first paint waits on the 11 MB esbuild download and the toolchain boot; the preview then
 // compiles on a 2 s poll, so the whole chain is slower than the suite's default expect timeout.
 const PREVIEW_TIMEOUT = 60_000;
@@ -165,4 +200,49 @@ test.describe('playground', () => {
     await expect(playground.preview.getByText('Shown Measure')).toBeVisible();
     await expect(playground.preview.getByText('Hidden Measure')).toHaveCount(0);
   });
+
+  test('should leave the measure on a dynamic question the respondent never saw out of the summary', async ({
+    page,
+    uniqueId
+  }) => {
+    const title = `Dynamic Measure ${uniqueId}`;
+    const playground = new PlaygroundPage(page);
+    await playground.goto(
+      generatePlaygroundURL({
+        baseURL: playgroundURL,
+        files: [{ content: dynamicMeasureInstrumentSource(title), name: 'index.ts' }],
+        label: title
+      })
+    );
+
+    await playground.preview.getByRole('button', { name: 'Begin' }).click({ timeout: PREVIEW_TIMEOUT });
+    // The radio items carry stable ids (`<name>-true`), unlike their labels, which libui translates.
+    await playground.preview.locator('#hasPet-false').click();
+    await playground.preview.getByRole('button', { name: 'Submit' }).click();
+
+    await expect(playground.preview.getByText('Has Pet Measure')).toBeVisible();
+    await expect(playground.preview.getByText('Pet Name Measure')).toHaveCount(0);
+  });
+
+  test('should list the measure on a dynamic question in the summary once the respondent reveals it', async ({
+    page,
+    uniqueId
+  }) => {
+    const title = `Dynamic Measure ${uniqueId}`;
+    const playground = new PlaygroundPage(page);
+    await playground.goto(
+      generatePlaygroundURL({
+        baseURL: playgroundURL,
+        files: [{ content: dynamicMeasureInstrumentSource(title), name: 'index.ts' }],
+        label: title
+      })
+    );
+
+    await playground.preview.getByRole('button', { name: 'Begin' }).click({ timeout: PREVIEW_TIMEOUT });
+    await playground.preview.locator('#hasPet-true').click();
+    await playground.preview.getByLabel('Pet Name', { exact: true }).fill('Rex');
+    await playground.preview.getByRole('button', { name: 'Submit' }).click();
+
+    await expect(playground.preview.getByText('Pet Name Measure')).toBeVisible();
+  });
 });