diff --git a/public/boardViewer.html b/public/boardViewer.html
index a9f83d8..2699078 100644
--- a/public/boardViewer.html
+++ b/public/boardViewer.html
@@ -251,7 +251,15 @@ const gCompareLines = new THREE.Group();   // Verbindungslinien Pos A↔Pos B
 const gPositionC    = new THREE.Group();   // Pos C Marker (nur fremd, cyan)
 const gYAxis        = new THREE.Group();   // Y-Achse Visualisierung (Kreismittelpunkte, Achse)
 const gSkeleton     = new THREE.Group();   // Roboter-Skeleton (FK, nur im Homing-Mode)
-scene.add(gPaper, gMarkers, gMeasured, gCameras, gCompare, gCompareLines, gPositionC, gYAxis, gSkeleton);
+const gArmMarkers   = new THREE.Group();   // Arm-Marker Modellpositionen + Fehlerlinien (FK)
+scene.add(gPaper, gMarkers, gMeasured, gCameras, gCompare, gCompareLines, gPositionC, gYAxis, gSkeleton, gArmMarkers);
+
+const LINK_COLORS = {
+  Board: 0x8b6528, Base: 0x888888,
+  Arm1: 0x3355cc, Ellbow: 0xaaaaaa, Arm2: 0xddcc88,
+  Hand: 0xcc8833, Palm: 0xcc3333,
+  FingerA: 0x33aa33, FingerB: 0x33aa33,
+};
 
 // ── Zustand für Positionen ────────────────────────────────────────────────────
 let _primaryFremdMarkers  = [];   // Pos A – [{marker_id, position_mm, num_cameras}]
@@ -259,8 +267,9 @@ let _compareFremdMarkers  = [];   // Pos B – [{marker_id, position_mm, num_cam
 let _positionCFremdMarkers = [];  // Pos C – [{marker_id, position_mm, num_cameras}]
 
 // ── Homing-Mode Zustand ───────────────────────────────────────────────────────
-let _currentRobot  = null;   // robot.json nach loadData()
-let _homingAngles  = null;   // { x, y, z, a, b, c, e } nach Homing-Run
+let _currentRobot    = null;   // robot.json nach loadData()
+let _homingAngles    = null;   // { x, y, z, a, b, c, e } nach Homing-Run
+let _measuredMarkers = null;   // measuredMarkers aus letztem buildScene-Aufruf
 
 // ── Roboter-Skeleton (Forward Kinematics) ─────────────────────────────────────
 /**
@@ -270,6 +279,7 @@ let _homingAngles  = null;   // { x, y, z, a, b, c, e } nach Homing-Run
  */
 function buildSkeletonFK(robot, angles) {
   clearGroup(gSkeleton);
+  clearGroup(gArmMarkers);
   if (!robot?.links) return;
 
   const links = robot.links;
@@ -310,23 +320,54 @@ function buildSkeletonFK(robot, angles) {
 
     // 3. Skeleton-Segment zeichnen
     const skel = link.skeleton;
-    if (!skel?.from || !skel?.to) continue;
+    if (skel?.from && skel?.to) {
+      const [fx, fy, fz] = skel.from;
+      const [tx, ty, tz] = skel.to;
+      const fromW = new THREE.Vector3(fx * S, fz * S, -fy * S).applyMatrix4(childFrame);
+      const toW   = new THREE.Vector3(tx * S, tz * S, -ty * S).applyMatrix4(childFrame);
 
-    const [fx, fy, fz] = skel.from;
-    const [tx, ty, tz] = skel.to;
-    const fromW = new THREE.Vector3(fx * S, fz * S, -fy * S).applyMatrix4(childFrame);
-    const toW   = new THREE.Vector3(tx * S, tz * S, -ty * S).applyMatrix4(childFrame);
+      const [cr, cg, cb] = skel.color ?? [0.8, 0.2, 0.2];
+      const color = new THREE.Color(cr, cg, cb);
+      const rad   = Math.max((skel.radius ?? 4) * S, 0.004);
 
-    const [cr, cg, cb] = skel.color ?? [0.8, 0.2, 0.2];
-    const color = new THREE.Color(cr, cg, cb);
-    const rad   = Math.max((skel.radius ?? 4) * S, 0.004);
+      gSkeleton.add(makeLine(fromW, toW, color, 0.9));
+      gSkeleton.add(makeSphere(fromW, rad, color));
+      gSkeleton.add(makeSphere(toW,   rad, color));
+      // Gelenk-Mittelpunkt (Welt-Ursprung des Link-Frames)
+      const jointW = new THREE.Vector3().applyMatrix4(childFrame);
+      gSkeleton.add(makeSphere(jointW, 0.004, 0xc8cdd8));
+    }
 
-    gSkeleton.add(makeLine(fromW, toW, color, 0.9));
-    gSkeleton.add(makeSphere(fromW, rad, color));
-    gSkeleton.add(makeSphere(toW,   rad, color));
-    // Gelenk-Mittelpunkt (Welt-Ursprung des Link-Frames)
-    const jointW = new THREE.Vector3().applyMatrix4(childFrame);
-    gSkeleton.add(makeSphere(jointW, 0.004, 0xc8cdd8));
+    // 4. Arm-Marker zeichnen (Modellposition via FK, als orientiertes Quadrat)
+    if (link.markers?.length > 0) {
+      const col = LINK_COLORS[linkName] ?? 0xffffff;
+      for (const m of link.markers) {
+        if (!m.position) continue;
+        const [lx, ly, lz] = m.position;
+        const posWorld = new THREE.Vector3(lx * S, lz * S, -ly * S).applyMatrix4(childFrame);
+        const markerSizeM = (m.size ?? 25) * S;
+        const [nx, ny, nz] = m.normal ?? [0, 0, 1];
+        const normalWorld = new THREE.Vector3(nx, nz, -ny).transformDirection(childFrame);
+        gArmMarkers.add(makeMarkerSquareOriented(posWorld, normalWorld, markerSizeM, col));
+        gArmMarkers.add(makeSphere(posWorld, 0.003, col));
+      }
+    }
+  }
+
+  // 5. Fehlerlinien: Modell-Marker → gemessene Position (aus 3b)
+  if (_measuredMarkers?.markers?.length > 0) {
+    for (const obs of _measuredMarkers.markers) {
+      if (obs.link === 'Board' || !obs.link) continue;
+      const ldata = links[obs.link];
+      if (!ldata || !frames[obs.link]) continue;
+      const modelM = ldata.markers?.find(mm => mm.id === obs.marker_id);
+      if (!modelM?.position) continue;
+      const [lx, ly, lz] = modelM.position;
+      const modelPosW = new THREE.Vector3(lx * S, lz * S, -ly * S).applyMatrix4(frames[obs.link]);
+      const obsPosW = r2vArr(obs.position_mm);
+      gArmMarkers.add(makeLine(modelPosW, obsPosW, 0xff8800, 0.85));
+      gArmMarkers.add(makeSphere(obsPosW, 0.007, LINK_COLORS[obs.link] ?? 0x3b82f6));
+    }
   }
 }
 
@@ -362,6 +403,18 @@ function makeMarkerSquare(pos, size, color) {
   return m;
 }
 
+function makeMarkerSquareOriented(pos, normalVec, size, color) {
+  const geo  = new THREE.PlaneGeometry(size, size);
+  const mat  = new THREE.MeshPhongMaterial({ color, side: THREE.DoubleSide, transparent: true, opacity: 0.85 });
+  const mesh = new THREE.Mesh(geo, mat);
+  mesh.position.copy(pos);
+  const n = normalVec.clone().normalize();
+  if (n.lengthSq() > 1e-9) {
+    mesh.quaternion.setFromUnitVectors(new THREE.Vector3(0, 0, 1), n);
+  }
+  return mesh;
+}
+
 function makeEdgeBorder(pos, size, color) {
   const geo = new THREE.EdgesGeometry(new THREE.PlaneGeometry(size, size));
   const mat = new THREE.LineBasicMaterial({ color, transparent: true, opacity: 0.75 });
@@ -404,6 +457,7 @@ function buildScene(data) {
   clearGroup(gPaper); clearGroup(gMarkers); clearGroup(gMeasured); clearGroup(gCameras);
 
   const { robot, detections, cameraPoses, measuredMarkers } = data;
+  _measuredMarkers = measuredMarkers ?? null;
 
   // Alle erkannten Marker-IDs (über alle Kameras)
   const detectedIds = new Set();
diff --git a/server/server.js b/server/server.js
index 745a7ce..547c7b3 100755
--- a/server/server.js
+++ b/server/server.js
@@ -446,6 +446,8 @@ const SCRIPT_4B     = path.join(__dirname, '..', 'scripts', '4b_revolute_angle.p
  */
 function runScript(args, send) {
   return new Promise((resolve) => {
+    const cmd = [PYTHON_BIN, '-u', ...args].join(' ');
+    console.log(`[runScript] ${cmd}`);
     const proc = spawn(PYTHON_BIN, ['-u', ...args]);
 
     let outBuf = '';