diff --git a/routes/operations.js b/routes/operations.js
index be397fe..38c1426 100644
--- a/routes/operations.js
+++ b/routes/operations.js
@@ -282,5 +282,82 @@ module.exports = function(pool) {
         }
     });
 
+    // list log entries for a version, newest first, with row counts
+    router.get('/versions/:id/log', async (req, res) => {
+        const versionId = parseInt(req.params.id);
+        try {
+            const verResult = await pool.query(
+                `SELECT v.*, s.tname FROM pf.version v JOIN pf.source s ON s.id = v.source_id WHERE v.id = $1`,
+                [versionId]
+            );
+            if (!verResult.rows.length) return res.status(404).json({ error: 'Version not found' });
+            const table = fcTable(verResult.rows[0].tname, versionId);
+            const result = await pool.query(`
+                SELECT l.*, count(f.pf_id)::int AS row_count
+                FROM pf.log l
+                LEFT JOIN ${table} f ON f.pf_logid = l.id
+                WHERE l.version_id = $1
+                GROUP BY l.id
+                ORDER BY l.id DESC
+            `, [versionId]);
+            res.json(result.rows);
+        } catch (err) {
+            console.error(err);
+            res.status(err.status || 500).json({ error: err.message });
+        }
+    });
+
+    // undo a log entry — delete all fc rows with this logid, then delete the log entry
+    router.delete('/log/:logid', async (req, res) => {
+        const logId = parseInt(req.params.logid);
+        try {
+            const logResult = await pool.query(`
+                SELECT l.*, v.status, s.tname, v.id AS version_id
+                FROM pf.log l
+                JOIN pf.version v ON v.id = l.version_id
+                JOIN pf.source s ON s.id = v.source_id
+                WHERE l.id = $1
+            `, [logId]);
+            if (!logResult.rows.length) return res.status(404).json({ error: 'Log entry not found' });
+            const log = logResult.rows[0];
+            if (log.status === 'closed') return res.status(403).json({ error: 'Version is closed' });
+            const table = fcTable(log.tname, log.version_id);
+            const client = await pool.connect();
+            try {
+                await client.query('BEGIN');
+                const deleted = await client.query(
+                    `DELETE FROM ${table} WHERE pf_logid = $1 RETURNING pf_id`, [logId]
+                );
+                await client.query('DELETE FROM pf.log WHERE id = $1', [logId]);
+                await client.query('COMMIT');
+                res.json({ rows_deleted: deleted.rowCount });
+            } catch (err) {
+                await client.query('ROLLBACK');
+                throw err;
+            } finally {
+                client.release();
+            }
+        } catch (err) {
+            console.error(err);
+            res.status(err.status || 500).json({ error: err.message });
+        }
+    });
+
+    // update the note on a log entry
+    router.patch('/log/:logid', async (req, res) => {
+        const logId = parseInt(req.params.logid);
+        const { note } = req.body;
+        try {
+            const result = await pool.query(
+                `UPDATE pf.log SET note = $1 WHERE id = $2 RETURNING *`, [note, logId]
+            );
+            if (!result.rows.length) return res.status(404).json({ error: 'Log entry not found' });
+            res.json(result.rows[0]);
+        } catch (err) {
+            console.error(err);
+            res.status(err.status || 500).json({ error: err.message });
+        }
+    });
+
     return router;
 };
diff --git a/ui/src/views/Forecast.jsx b/ui/src/views/Forecast.jsx
index 30acef1..1ed44fb 100644
--- a/ui/src/views/Forecast.jsx
+++ b/ui/src/views/Forecast.jsx
@@ -58,6 +58,13 @@ export default function Forecast() {
 
   const [panelWidth, setPanelWidth] = useState(224)
 
+  // history modal
+  const [showLog,       setShowLog]       = useState(false)
+  const [logEntries,    setLogEntries]    = useState([])
+  const [logLoading,    setLogLoading]    = useState(false)
+  const [editingNote,   setEditingNote]   = useState(null)  // { id, text }
+  const [undoingId,     setUndoingId]     = useState(null)
+
   const viewerRef      = useRef(null)
   const workerRef      = useRef(null)
   const tableRef       = useRef(null)
@@ -323,6 +330,49 @@ export default function Forecast() {
     setTimeout(() => setMsg(null), 3000)
   }
 
+  async function openLog() {
+    setShowLog(true)
+    setLogLoading(true)
+    try {
+      const data = await fetch(`/api/versions/${versionId}/log`).then(r => r.json())
+      setLogEntries(data)
+    } catch (err) {
+      flash(err.message, 'error')
+    } finally {
+      setLogLoading(false)
+    }
+  }
+
+  async function undoEntry(logId) {
+    setUndoingId(logId)
+    try {
+      const res  = await fetch(`/api/log/${logId}`, { method: 'DELETE' })
+      const data = await res.json()
+      if (!res.ok) { flash(data.error, 'error'); return }
+      setLogEntries(prev => prev.filter(e => e.id !== logId))
+      flash(`Undone — ${data.rows_deleted} rows removed`)
+      initViewer(versionId, sourceId)
+    } catch (err) {
+      flash(err.message, 'error')
+    } finally {
+      setUndoingId(null)
+    }
+  }
+
+  async function saveNote(logId, text) {
+    try {
+      const res  = await fetch(`/api/log/${logId}`, {
+        method: 'PATCH', headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ note: text })
+      })
+      if (!res.ok) { flash('Failed to save note', 'error'); return }
+      setLogEntries(prev => prev.map(e => e.id === logId ? { ...e, note: text } : e))
+      setEditingNote(null)
+    } catch (err) {
+      flash(err.message, 'error')
+    }
+  }
+
   const selectedVersion = versions.find(v => String(v.id) === versionId)
   const dimCols  = colMetaRef.current.filter(c => c.role === 'dimension')
   const hasSlice = Object.keys(slice).length > 0
@@ -393,6 +443,11 @@ export default function Forecast() {
           <button onClick={resetLayout} className="text-xs text-gray-300 hover:text-gray-500">reset</button>
         )}
 
+        <button onClick={openLog} disabled={!versionId}
+          className="text-xs border border-gray-200 rounded px-2 py-0.5 text-gray-500 hover:bg-gray-50 disabled:opacity-40">
+          History
+        </button>
+
         {/* Depth controls */}
         <div className="ml-auto flex items-center gap-1.5">
           <span className="text-xs text-gray-400">depth</span>
@@ -410,6 +465,82 @@ export default function Forecast() {
         </div>
       </div>
 
+      {/* History modal */}
+      {showLog && (
+        <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/40" onClick={() => setShowLog(false)}>
+          <div className="bg-white rounded-lg shadow-xl w-full max-w-4xl mx-4 flex flex-col max-h-[80vh]" onClick={e => e.stopPropagation()}>
+            <div className="flex items-center justify-between px-5 py-3 border-b border-gray-200 shrink-0">
+              <span className="font-medium text-gray-700 text-sm">Change History</span>
+              <button onClick={() => setShowLog(false)} className="text-gray-400 hover:text-gray-600 text-lg leading-none">×</button>
+            </div>
+
+            <div className="overflow-y-auto flex-1">
+              {logLoading ? (
+                <div className="p-8 text-center text-sm text-gray-400">Loading…</div>
+              ) : logEntries.length === 0 ? (
+                <div className="p-8 text-center text-sm text-gray-400">No log entries yet.</div>
+              ) : (
+                <table className="w-full text-xs border-collapse">
+                  <thead className="sticky top-0 bg-gray-50 text-gray-400 uppercase tracking-wide" style={{fontSize:'10px'}}>
+                    <tr>
+                      <th className="text-left px-4 py-2 font-medium w-32">Time</th>
+                      <th className="text-left px-4 py-2 font-medium w-24">Op</th>
+                      <th className="text-left px-4 py-2 font-medium">Slice</th>
+                      <th className="text-left px-4 py-2 font-medium">Note</th>
+                      <th className="text-right px-4 py-2 font-medium w-16">Rows</th>
+                      <th className="px-4 py-2 w-16"></th>
+                    </tr>
+                  </thead>
+                  <tbody>
+                    {logEntries.map(entry => (
+                      <tr key={entry.id} className="border-t border-gray-100 hover:bg-gray-50">
+                        <td className="px-4 py-2 text-gray-400 whitespace-nowrap">{fmtStamp(entry.stamp)}</td>
+                        <td className="px-4 py-2">
+                          <span className={`px-1.5 py-0.5 rounded text-xs font-medium ${opBadge(entry.operation)}`}>
+                            {entry.operation}
+                          </span>
+                        </td>
+                        <td className="px-4 py-2 text-gray-600 font-mono">{fmtSlice(entry.slice)}</td>
+                        <td className="px-4 py-2 text-gray-600 max-w-xs">
+                          {editingNote?.id === entry.id ? (
+                            <div className="flex items-center gap-1">
+                              <input autoFocus value={editingNote.text}
+                                onChange={e => setEditingNote(n => ({ ...n, text: e.target.value }))}
+                                onKeyDown={e => {
+                                  if (e.key === 'Enter') saveNote(entry.id, editingNote.text)
+                                  if (e.key === 'Escape') setEditingNote(null)
+                                }}
+                                className="border border-blue-300 rounded px-1.5 py-0.5 text-xs flex-1 focus:outline-none" />
+                              <button onClick={() => saveNote(entry.id, editingNote.text)} className="text-blue-600 hover:text-blue-800">✓</button>
+                              <button onClick={() => setEditingNote(null)} className="text-gray-400 hover:text-gray-600">✕</button>
+                            </div>
+                          ) : (
+                            <span onClick={() => setEditingNote({ id: entry.id, text: entry.note || '' })}
+                              className="cursor-text hover:bg-blue-50 rounded px-1 -mx-1 block truncate"
+                              title={entry.note || 'Click to add note'}>
+                              {entry.note || <span className="text-gray-300 italic">add note</span>}
+                            </span>
+                          )}
+                        </td>
+                        <td className="px-4 py-2 text-right text-gray-500 tabular-nums">{entry.row_count ?? '—'}</td>
+                        <td className="px-4 py-2">
+                          <button
+                            onClick={() => undoEntry(entry.id)}
+                            disabled={undoingId === entry.id}
+                            className="text-xs border border-red-200 text-red-400 hover:text-red-600 hover:border-red-400 rounded px-2 py-0.5 disabled:opacity-40 whitespace-nowrap">
+                            {undoingId === entry.id ? '…' : 'Undo'}
+                          </button>
+                        </td>
+                      </tr>
+                    ))}
+                  </tbody>
+                </table>
+              )}
+            </div>
+          </div>
+        </div>
+      )}
+
       {/* Main area */}
       <div className="flex-1 flex min-h-0">
         {/* Perspective viewer */}
@@ -539,6 +670,24 @@ export default function Forecast() {
 
 const inp = 'border border-gray-200 rounded px-2 py-1 text-xs flex-1 bg-white min-w-0'
 
+function fmtStamp(stamp) {
+  return new Date(stamp).toLocaleString(undefined, { month: 'short', day: 'numeric', hour: 'numeric', minute: '2-digit' })
+}
+
+function fmtSlice(slice) {
+  if (!slice || !Object.keys(slice).length) return '—'
+  return Object.entries(slice).map(([k, v]) => `${k} = ${v}`).join(', ')
+}
+
+const OP_BADGE = {
+  baseline:  'bg-gray-100 text-gray-600',
+  reference: 'bg-blue-50 text-blue-600',
+  scale:     'bg-green-50 text-green-700',
+  recode:    'bg-amber-50 text-amber-700',
+  clone:     'bg-purple-50 text-purple-700',
+}
+function opBadge(op) { return OP_BADGE[op] || 'bg-gray-100 text-gray-500' }
+
 function Row({ label, children }) {
   return (
     <div className="flex items-center gap-2">