diff --git a/config/jupiter_grs.json b/config/jupiter_grs.json
index e1c8ff3..a9f2f7a 100644
--- a/config/jupiter_grs.json
+++ b/config/jupiter_grs.json
@@ -1,6 +1,32 @@
 {
-    "refDate": "2026-04-13T00:31:40.897Z",
-    "refAngle": 312227.6287687423,
-    "calibratedAt": "2026-04-12T09:26:52+00:00",
-    "calibratedBy": "Eskimue"
+    "refDate": "2026-04-13T04:07:00.000Z",
+    "refAngle": 312229.88248732366,
+    "calibratedAt": "2026-04-12T09:35:41+00:00",
+    "calibratedBy": "Eskimue",
+    "history": [
+        {
+            "refDate": "2025-04-12T01:08:00.000Z",
+            "refAngle": 306668.75732167566,
+            "calibratedAt": "2026-04-12T09:33:58+00:00",
+            "calibratedBy": "Eskimue"
+        },
+        {
+            "refDate": "2026-01-01T09:49:00.000Z",
+            "refAngle": 310684.2913082397,
+            "calibratedAt": "2026-04-12T09:38:07+00:00",
+            "calibratedBy": "Eskimue"
+        },
+        {
+            "refDate": "2026-04-12T08:15:00.000Z",
+            "refAngle": 312217.3093069398,
+            "calibratedAt": "2026-04-12T09:32:29+00:00",
+            "calibratedBy": "Eskimue"
+        },
+        {
+            "refDate": "2026-04-13T04:07:00.000Z",
+            "refAngle": 312229.88248732366,
+            "calibratedAt": "2026-04-12T09:35:41+00:00",
+            "calibratedBy": "Eskimue"
+        }
+    ]
 }
\ No newline at end of file
diff --git a/public/jupitersystem.php b/public/jupitersystem.php
index 34369e8..9a667b5 100644
--- a/public/jupitersystem.php
+++ b/public/jupitersystem.php
@@ -24,12 +24,26 @@ if (isset($_GET['grs_api'])) {
         if (!$isAdmin) { http_response_code(403); echo json_encode(['error' => 'Nicht autorisiert']); exit; }
         $body = json_decode(file_get_contents('php://input'), true);
         if (!$body || !isset($body['refDate'], $body['refAngle'])) { http_response_code(400); echo json_encode(['error' => 'Ungültige Daten']); exit; }
-        $data = [
+        $existing = [];
+        if (file_exists($dataFile)) {
+            $existing = json_decode(file_get_contents($dataFile), true) ?? [];
+        }
+        $history = $existing['history'] ?? [];
+        $history[] = [
             'refDate'      => (string) $body['refDate'],
             'refAngle'     => (float)  $body['refAngle'],
             'calibratedAt' => date('c'),
             'calibratedBy' => $_SESSION['username'] ?? 'admin',
         ];
+        usort($history, fn($a, $b) => strcmp((string) $a['refDate'], (string) $b['refDate']));
+        $latest = end($history);
+        $data = [
+            'refDate'      => $latest['refDate'],
+            'refAngle'     => $latest['refAngle'],
+            'calibratedAt' => $latest['calibratedAt'],
+            'calibratedBy' => $latest['calibratedBy'],
+            'history'      => $history,
+        ];
         $written = file_put_contents($dataFile, json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE));
         echo $written !== false ? json_encode(['ok' => true]) : json_encode(['error' => 'Schreibfehler – Dateiberechtigung prüfen']);
         exit;
@@ -140,6 +154,15 @@ $bodyClass = 'solarsystem-page jupitersystem-page';
                         <button class="btn btn-secondary btn-full mt-md" id="grsBtnShadowRays">Schattenstrahlen anzeigen</button>
                         <button class="btn btn-primary btn-full mt-xs" id="grsBtnSave">Kalibrierung speichern</button>
                         <div id="grsCalibStatus" class="hint inline-fade mt-sm"></div>
+
+                        <div id="grsDriftSection" style="display:none">
+                            <div class="solarsystem-label mt-md">GRS Drift-Historie</div>
+                            <p class="hint mt-2xs">Abweichung vom System-II-Rhythmus zwischen je zwei Abgleichen.</p>
+                            <div id="grsDriftAvg" class="hint mt-2xs" style="color:var(--gold-pale)"></div>
+                            <div style="overflow-x:auto;margin-top:0.5rem">
+                                <table id="grsDriftTable" class="data-table" style="font-size:0.8rem;white-space:nowrap"></table>
+                            </div>
+                        </div>
                     </div>
                 </details>
             </div>
@@ -779,6 +802,60 @@ function parseGrsTransitInput(str) {
   return isNaN(d.getTime()) ? null : d;
 }
 
+function renderGrsDrift(history) {
+  const section = document.getElementById('grsDriftSection');
+  const table   = document.getElementById('grsDriftTable');
+  const avgEl   = document.getElementById('grsDriftAvg');
+  if (!section || !table || !avgEl || !Array.isArray(history) || history.length < 2) {
+    if (section) section.style.display = 'none';
+    return;
+  }
+
+  const RAD_TO_DEG = 180 / Math.PI;
+
+  let rows = '';
+  const driftRates = [];
+
+  for (let i = 1; i < history.length; i++) {
+    const prev = history[i - 1];
+    const curr = history[i];
+    const t1 = new Date(prev.refDate).getTime();
+    const t2 = new Date(curr.refDate).getTime();
+    const elapsedDays = (t2 - t1) / 86400000;
+    if (elapsedDays <= 0) continue;
+
+    const expectedDeg = (elapsedDays / GRS_SYSTEM_II_PERIOD_DAYS) * 360;
+    const actualDeg   = (curr.refAngle - prev.refAngle) * RAD_TO_DEG;
+    // Drift auf den Bereich [-180, 180] normieren
+    let drift = ((actualDeg - expectedDeg) % 360 + 540) % 360 - 180;
+    const driftPerDay = drift / elapsedDays;
+    driftRates.push(driftPerDay);
+
+    const sign  = driftPerDay >= 0 ? '+' : '';
+    const color = Math.abs(driftPerDay) < 0.05 ? 'var(--text-dim)' : (driftPerDay > 0 ? 'var(--gold-pale)' : 'var(--cyan)');
+    const dateStr = new Date(curr.refDate).toLocaleString('de-DE', { timeZone: 'UTC', dateStyle: 'short', timeStyle: 'short' });
+
+    rows += `<tr>
+      <td>${dateStr} UT</td>
+      <td>${elapsedDays.toFixed(1)} d</td>
+      <td style="color:${color};font-variant-numeric:tabular-nums">${sign}${drift.toFixed(2)}°</td>
+      <td style="color:${color};font-variant-numeric:tabular-nums">${sign}${driftPerDay.toFixed(3)}°/d</td>
+    </tr>`;
+  }
+
+  table.innerHTML = `<thead><tr>
+    <th>Abgleich</th><th>Abstand</th><th>Drift ges.</th><th>Drift/Tag</th>
+  </tr></thead><tbody>${rows}</tbody>`;
+
+  if (driftRates.length > 0) {
+    const avg = driftRates.reduce((s, v) => s + v, 0) / driftRates.length;
+    const sign = avg >= 0 ? '+' : '';
+    avgEl.textContent = `Ø Drift: ${sign}${avg.toFixed(3)}°/Tag`;
+  }
+
+  section.style.display = '';
+}
+
 function formatGrsStatus(data) {
   if (!data.calibratedAt) return 'Noch keine Kalibrierung gespeichert.';
   const at = new Date(data.calibratedAt).toLocaleString('de-DE', { timeZone: 'UTC', dateStyle: 'short', timeStyle: 'short' });
@@ -797,6 +874,7 @@ async function loadGrsCalibration() {
     }
     const statusEl = document.getElementById('grsCalibStatus');
     if (statusEl) statusEl.textContent = formatGrsStatus(data);
+    renderGrsDrift(data.history);
   } catch (e) {}
 }
 
@@ -948,6 +1026,12 @@ function attachAdminHandlers() {
   grsBtnRot5R.addEventListener('click', () => shiftGrsRotation(5));
 
   grsBtnSave.addEventListener('click', async () => {
+    if (grsTransitInput.value.trim() === '') {
+      grsParseError.textContent = 'Bitte zuerst einen GRS-Transitzeitpunkt eingeben und auf „Auf diese Zeit setzen" klicken.';
+      grsParseError.classList.remove('is-hidden');
+      return;
+    }
+
     const elapsedDays = (simDate - grsRefDate) / 86400000;
     grsRefAngle = grsRefAngle + (elapsedDays / GRS_SYSTEM_II_PERIOD_DAYS) * Math.PI * 2;
     grsRefDate = new Date(simDate);
@@ -956,6 +1040,10 @@ function attachAdminHandlers() {
     grsCalibStatus.textContent = ok === true
       ? `Gespeichert: ${simDate.toISOString().slice(0, 16).replace('T', ' ')} UT\nFür alle Nutzer aktiv.`
       : `Fehler: ${ok}`;
+    if (ok === true) {
+      const res = await fetch('jupitersystem.php?grs_api').catch(() => null);
+      if (res && res.ok) { const d = await res.json(); renderGrsDrift(d.history); }
+    }
   });
 }