diff --git a/obr/index.html b/obr/index.html
index f3235d6..3cee4fe 100644
--- a/obr/index.html
+++ b/obr/index.html
@@ -239,9 +239,12 @@ <h4>Worked example</h4>
           <em>spending</em> shock (<code>CGG</code>) lands straight in the GDP
           identity with no behavioural equation responding, giving a multiplier
           of exactly <strong>1.0000</strong>, flat, against the OBR's 0.6 &mdash;
-          and capital spending (<code>CGIPS</code>) is worse, moving business
-          investment <strong>&minus;292% of the shock</strong>, wrong-signed
-          against the OBR's 1.0. The
+          and capital spending (<code>CGIPS</code>) is worse still: it does not
+          transmit at all. Total fixed investment moves exactly zero, and
+          business investment moves wrong-signed and
+          <strong>non-proportionally</strong> &mdash; quadrupling the shock
+          changes the response by under a factor of two, so there is no
+          multiplier to quote, against the OBR's published 1.0. The
           <a href="/obr/validation#caveats">validation page</a> lists the
           full set of known limits.
         </div>
diff --git a/obr/validation/index.html b/obr/validation/index.html
index d53f697..2be9225 100644
--- a/obr/validation/index.html
+++ b/obr/validation/index.html
@@ -74,11 +74,26 @@ <h1 class="reveal page-title" style="--d:1;">
     </div>
   </nav>
 
-  <section id="trust" class="band">
+  <section class="band band-wide">
     <div class="band-head">
-      <span class="kicker mono">how far to trust it</span>
-      <h2>Excellent anchored. Weak free-running. Both published.</h2>
+      <span class="kicker mono">validation</span>
+      <h2>How far to trust it, and where it stops.</h2>
     </div>
+    <div class="prose">
+      <p>
+        Five steps: what the three configurations score, the anchored fit
+        against the OBR's own forecast, the one independent test, what the
+        equations do free-running with no OBR judgement, and the limits that
+        follow. The panel alongside carries the figures each step refers to.
+      </p>
+    </div>
+
+    <div class="scrolly-wrap">
+      <div class="scrolly-steps">
+
+      <div class="meth-step" id="trust" data-step="0">
+        <div class="meth-step-head"><span class="meth-step-num mono">1</span><h3>How far to trust it</h3></div>
+        <p class="mo-lead">Excellent anchored. Weak free-running. Both published.</p>
     <div class="prose">
       <p>
         Three configurations, three levels of trust. Errors are MAPE (mean
@@ -141,13 +156,17 @@ <h2>Excellent anchored. Weak free-running. Both published.</h2>
         Office for Budget Responsibility, and not official OBR estimates.
       </p>
     </div>
-  </section>
-
-  <section id="anchored" class="band">
-    <div class="band-head">
-      <span class="kicker mono">evidence — anchored</span>
-      <h2>Against the OBR's own forecast, and HMRC's reckoner.</h2>
-    </div>
+        <div class="meth-inline">
+        <div class="meth-sec-title">the three configurations</div>
+        <div class="meth-eq"><div class="meth-eq-label">anchored</div><div class="meth-eq-body">GDP 0.15% MAPE, consumption 0.25% &mdash; by construction, not skill</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">held add-factors</div><div class="meth-eq-body">GDP 0.37%, 6 of 8 computed in band</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">free-running</div><div class="meth-eq-body">GDP 4.48%, consumption 7.49% &mdash; report-only</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">CI gate</div><div class="meth-eq-body">the build hard-fails if anchored GDP drifts past 1%</div></div>
+        </div>
+      </div>
+      <div class="meth-step" id="anchored" data-step="1">
+        <div class="meth-step-head"><span class="meth-step-num mono">2</span><h3>Anchored against the EFO</h3></div>
+        <p class="mo-lead">One test, not two.</p>
     <div class="prose">
       <p>
         Anchored GDP and consumption are <strong>one test, not two</strong>:
@@ -206,6 +225,18 @@ <h2>Against the OBR's own forecast, and HMRC's reckoner.</h2>
 </svg>
         <figcaption>Current March 2026 EFO baseline. Quarterly deviation from the published EFO; CI hard-fails at &#177;1.00%, off the top and bottom of this frame. Computed from <code>papers/obr-macro/figures/fig_anchored_data.csv</code>, regenerated from the March 2026 detailed forecast tables on 21 July 2026.</figcaption>
       </figure>
+      </div>
+        <div class="meth-inline">
+        <div class="meth-sec-title">anchored fit</div>
+        <div class="meth-eq"><div class="meth-eq-label">real GDP</div><div class="meth-eq-body">0.15% MAPE, 2025Q1&ndash;2027Q4</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">consumption</div><div class="meth-eq-body">0.25% &mdash; the same &pound;m error as GDP, not a second test</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">why</div><div class="meth-eq-body">every other demand-identity term is exogenous or pinned</div></div>
+        </div>
+      </div>
+      <div class="meth-step" id="val-hmrc" data-step="2">
+        <div class="meth-step-head"><span class="meth-step-num mono">3</span><h3>The independent test</h3></div>
+        <p class="mo-lead">HMRC's own ready reckoner.</p>
+      <div class="prose">
       <p>
         A 1pp basic-rate rise from April 2026, costed through the PolicyEngine
         static-costing bridge: <strong>£6.46bn against HMRC's £6.9bn,
@@ -266,6 +297,18 @@ <h2>Against the OBR's own forecast, and HMRC's reckoner.</h2>
         </tbody>
       </table>
       </div>
+      </div>
+        <div class="meth-inline">
+        <div class="meth-sec-title">1p on the basic rate</div>
+        <div class="meth-eq"><div class="meth-eq-label">ours, 2026</div><div class="meth-eq-body">&pound;6.46bn</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">HMRC reckoner</div><div class="meth-eq-body">&pound;6.90bn &mdash; a &minus;6.4% gap</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">status</div><div class="meth-eq-body">a benchmark, not a validation</div></div>
+        </div>
+      </div>
+      <div class="meth-step" id="val-freerun" data-step="3">
+        <div class="meth-step-head"><span class="meth-step-num mono">4</span><h3>Free-running</h3></div>
+        <p class="mo-lead">What the equations do with no OBR judgement.</p>
+      <div class="prose">
       <figure class="vfig">
         <svg class="vchart" data-chart="obr-computed-share" viewBox="0 0 760 314" role="img" aria-labelledby="obr-computed-share-t obr-computed-share-d">
 <title id="obr-computed-share-t">How much of the OBR emulator scorecard the model actually computes</title>
@@ -435,13 +478,17 @@ <h2>Against the OBR's own forecast, and HMRC's reckoner.</h2>
         <a href="/obr">obr-macro model page →</a>
       </p>
     </div>
-  </section>
-
-  <section id="caveats" class="band">
-    <div class="band-head">
-      <span class="kicker mono">limits</span>
-      <h2>Known limitations.</h2>
-    </div>
+        <div class="meth-inline">
+        <div class="meth-sec-title">the honest scorecard</div>
+        <div class="meth-eq"><div class="meth-eq-label">real GDP</div><div class="meth-eq-body">4.48% MAPE &mdash; the model contracts while the EFO grows</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">computed</div><div class="meth-eq-body">11 of 21 headline variables; the other 10 are passthrough</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">in band</div><div class="meth-eq-body">6 of the 11, and one of those is a trivial identity</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">worst</div><div class="meth-eq-body">company profits 63.29%</div></div>
+        </div>
+      </div>
+      <div class="meth-step" id="caveats" data-step="4">
+        <div class="meth-step-head"><span class="meth-step-num mono">5</span><h3>Known limitations</h3></div>
+        <p class="mo-lead">What it cannot be used for.</p>
     <div class="prose">
       <div class="table-scroll mo-tablecard"><table>
         <caption>Known limits of the OBR emulator</caption>
@@ -489,8 +536,63 @@ <h2>Known limitations.</h2>
           </tr>
         </tbody>
       </table></div>
+    </div>
+        <div class="meth-inline">
+        <div class="meth-sec-title">the headline limits</div>
+        <div class="meth-eq"><div class="meth-eq-label">spending multiplier</div><div class="meth-eq-body"><code>CGG</code> is exactly 1.0000, flat, against the OBR's 0.6</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">capital spending</div><div class="meth-eq-body"><code>CGIPS</code> does not transmit &mdash; do not score it</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">corporation tax</div><div class="meth-eq-body"><code>TCPRO</code> converges slowly: 12 quarters is ~40% of plateau</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">inert blocks</div><div class="meth-eq-body">unemployment, prices and trade never respond to any lever</div></div>
+        <div class="meth-eq"><div class="meth-eq-label">convergence</div><div class="meth-eq-body">no quarter reaches tolerance &mdash; read scale, not quarters</div></div>
+        </div>
+      </div>
+
+      </div>
+
+      <aside class="scrolly-sticky" aria-hidden="true">
+        <div class="meth-panel" data-step="0">
+          <div class="meth-panel-head"><span class="meth-panel-title">How far to trust it</span><span class="meth-panel-badge mono">Step 1</span></div>
+          <div class="meth-sec-title">the three configurations</div>
+          <div class="meth-eq"><div class="meth-eq-label">anchored</div><div class="meth-eq-body">GDP 0.15% MAPE, consumption 0.25% &mdash; by construction, not skill</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">held add-factors</div><div class="meth-eq-body">GDP 0.37%, 6 of 8 computed in band</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">free-running</div><div class="meth-eq-body">GDP 4.48%, consumption 7.49% &mdash; report-only</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">CI gate</div><div class="meth-eq-body">the build hard-fails if anchored GDP drifts past 1%</div></div>
+        </div>
+        <div class="meth-panel" data-step="1" hidden>
+          <div class="meth-panel-head"><span class="meth-panel-title">Anchored against the EFO</span><span class="meth-panel-badge mono">Step 2</span></div>
+          <div class="meth-sec-title">anchored fit</div>
+          <div class="meth-eq"><div class="meth-eq-label">real GDP</div><div class="meth-eq-body">0.15% MAPE, 2025Q1&ndash;2027Q4</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">consumption</div><div class="meth-eq-body">0.25% &mdash; the same &pound;m error as GDP, not a second test</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">why</div><div class="meth-eq-body">every other demand-identity term is exogenous or pinned</div></div>
+        </div>
+        <div class="meth-panel" data-step="2" hidden>
+          <div class="meth-panel-head"><span class="meth-panel-title">The independent test</span><span class="meth-panel-badge mono">Step 3</span></div>
+          <div class="meth-sec-title">1p on the basic rate</div>
+          <div class="meth-eq"><div class="meth-eq-label">ours, 2026</div><div class="meth-eq-body">&pound;6.46bn</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">HMRC reckoner</div><div class="meth-eq-body">&pound;6.90bn &mdash; a &minus;6.4% gap</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">status</div><div class="meth-eq-body">a benchmark, not a validation</div></div>
+        </div>
+        <div class="meth-panel" data-step="3" hidden>
+          <div class="meth-panel-head"><span class="meth-panel-title">Free-running</span><span class="meth-panel-badge mono">Step 4</span></div>
+          <div class="meth-sec-title">the honest scorecard</div>
+          <div class="meth-eq"><div class="meth-eq-label">real GDP</div><div class="meth-eq-body">4.48% MAPE &mdash; the model contracts while the EFO grows</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">computed</div><div class="meth-eq-body">11 of 21 headline variables; the other 10 are passthrough</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">in band</div><div class="meth-eq-body">6 of the 11, and one of those is a trivial identity</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">worst</div><div class="meth-eq-body">company profits 63.29%</div></div>
+        </div>
+        <div class="meth-panel" data-step="4" hidden>
+          <div class="meth-panel-head"><span class="meth-panel-title">Known limitations</span><span class="meth-panel-badge mono">Step 5</span></div>
+          <div class="meth-sec-title">the headline limits</div>
+          <div class="meth-eq"><div class="meth-eq-label">spending multiplier</div><div class="meth-eq-body"><code>CGG</code> is exactly 1.0000, flat, against the OBR's 0.6</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">capital spending</div><div class="meth-eq-body"><code>CGIPS</code> does not transmit &mdash; do not score it</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">corporation tax</div><div class="meth-eq-body"><code>TCPRO</code> converges slowly: 12 quarters is ~40% of plateau</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">inert blocks</div><div class="meth-eq-body">unemployment, prices and trade never respond to any lever</div></div>
+          <div class="meth-eq"><div class="meth-eq-label">convergence</div><div class="meth-eq-body">no quarter reaches tolerance &mdash; read scale, not quarters</div></div>
+        </div>
+      </aside>
     </div>
   </section>
+
 </main>
 
 <footer class="foot foot-bar">
@@ -503,5 +605,42 @@ <h2>Known limitations.</h2>
 </footer>
 
 <script src="/reveal.js?v=2" defer></script>
+<script>
+// Validation scrollytelling: highlight the step at the reading line and
+// show its panel in the sticky aside.
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+      step.classList.toggle("active", i === active);
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+      return Number(panel.getAttribute("data-step"));
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+    panels.forEach(function (panel) {
+      var ds = Number(panel.getAttribute("data-step"));
+      if (ds <= active && ds > want) want = ds;
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+    panels.forEach(function (panel) {
+      panel.hidden = Number(panel.getAttribute("data-step")) !== want;
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+  window.addEventListener("resize", update, { passive: true });
+  window.addEventListener("hashchange", function () { setTimeout(update, 0); });
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 </html>