diff --git a/public/js/webgl-book-shape-lab.js b/public/js/webgl-book-shape-lab.js
index d75111f..dfe02aa 100644
--- a/public/js/webgl-book-shape-lab.js
+++ b/public/js/webgl-book-shape-lab.js
@@ -214,10 +214,11 @@ function rebuildBook() {
     const bundleCount = Math.max(4, Math.round(pageCount / 10));
     const spineWidth = calculateSpineWidth(bundleCount);
     const leftCount = calculateLeftBundleCount(bundleCount);
-    const hingeX = spineWidth * 0.5 + HINGE_INSET;
-    const foreEdgeX = spineWidth * 0.5 + pageWidth;
+    const spineHalf = spineArcHalf(spineWidth);
+    const hingeX = spineHalf + HINGE_INSET;
+    const foreEdgeX = spineHalf + pageWidth;
     const bundleSpacing = calculateBundleSpacing(bundleCount, spineWidth, leftCount);
-    activeSpineHalf = spineWidth * 0.5;
+    activeSpineHalf = spineHalf;
     const lines = simulatePageLines(bundleCount, pageWidth, pageSplineLength, spineWidth, foreEdgeX, bundleSpacing, leftCount);
     lastLengthError = measureLineLengthError(lines, pageSplineLength);
     lastSpacingError = measureStackSpacingError(lines, bundleSpacing);
@@ -245,7 +246,7 @@ function addCoverAssembly(pageWidth, depth, thickness, spineWidth) {
 }
 
 function createCoverAssemblyGeometry(pageWidth, depth, thickness, spineWidth) {
-    const spineHalf = spineWidth * 0.5;
+    const spineHalf = spineArcHalf(spineWidth);
     const hingeX = spineHalf + HINGE_INSET;
     const outerX = spineHalf + pageWidth + COVER_OVERHANG;
     const outerTopY = BOOK_PROFILE.tableY + thickness;
@@ -339,7 +340,7 @@ function createClothSpineGeometry(depth, spineWidth) {
 }
 
 function spineCurvePoint(t, spineWidth) {
-    const radiusX = spineWidth * 0.42;
+    const radiusX = spineArcHalf(spineWidth);
     const radiusY = 0.018;
     const baseY = BOOK_PROFILE.tableY + BOOK_PROFILE.coverThickness + 0.002;
     const theta = Math.PI * (1 - THREE.MathUtils.clamp(t, 0, 1));
@@ -350,6 +351,10 @@ function spineCurvePoint(t, spineWidth) {
     };
 }
 
+function spineArcHalf(spineWidth) {
+    return spineWidth * 0.42;
+}
+
 function calculateSpineWidth(bundleCount) {
     const minimumWidth = 0.16;
     if (bundleCount <= 1) return minimumWidth;
diff --git a/public/webgl-book-shape-lab.html b/public/webgl-book-shape-lab.html
index f48a61b..072e778 100644
--- a/public/webgl-book-shape-lab.html
+++ b/public/webgl-book-shape-lab.html
@@ -74,6 +74,6 @@
         <button id="fast_forward" type="button">Fast Forward</button>
         <output id="flip_count">0 / 10</output>
     </div>
-    <script type="module" src="/js/webgl-book-shape-lab.js?v=spline-length-foreedge-1"></script>
+    <script type="module" src="/js/webgl-book-shape-lab.js?v=task1-restored-1"></script>
 </body>
 </html>