diff --git a/web/MinesweeperPanel.tsx b/web/MinesweeperPanel.tsx
index 014c0c4..17bed45 100644
--- a/web/MinesweeperPanel.tsx
+++ b/web/MinesweeperPanel.tsx
@@ -82,6 +82,19 @@ export const MinesweeperPanel = () => {
   const [frame, setFrame] = useState<{ width: number; height: number } | null>(null);
   const [box, setBox] = useState<{ width: number; height: number; dpr: number; zoom: number } | null>(null);
   const [status, setStatus] = useState<SessionStatus | null>(null);
+  /*
+    TEMPORARY INSTRUMENTATION — press-to-paint, measured where it is actually felt.
+
+    The same figure taken at x11vnc's own socket is ~50ms (median 47ms over 8 synthetic presses, and 51ms
+    with the X DAMAGE extension enabled, so `-noxdamage` is not costing anything). What that number cannot
+    include is the two relay hops and the network, and those are the only places the rest of the lag can
+    be. This is the end-to-end figure, so the two can be subtracted.
+
+    Cleared on the frame that follows a press, so it times the first paint after a click rather than every
+    repaint. Delete this and its row below once the question is settled.
+  */
+  const pressAtRef = useRef<number | null>(null);
+  const [lagMs, setLagMs] = useState<number | null>(null);
   const [error, setError] = useState<string | null>(null);
   const [connected, setConnected] = useState(false);
   const [busy, setBusy] = useState(false);
@@ -200,6 +213,10 @@ export const MinesweeperPanel = () => {
       },
       onFrame: (image, x, y) => {
         canvasRef.current?.getContext('2d')?.putImageData(image, x, y);
+        if (pressAtRef.current !== null) {
+          setLagMs(Math.round(performance.now() - pressAtRef.current));
+          pressAtRef.current = null;
+        }
       },
       onCopyRect: (from, to) => {
         // Same canvas as source and destination, which is what CopyRect is: the 2D context takes a
@@ -301,7 +318,10 @@ export const MinesweeperPanel = () => {
     const rfb = rfbRef.current;
     if (!rfb) return;
     ev.preventDefault();
-    if (kind === 'down') ev.currentTarget.focus();
+    if (kind === 'down') {
+      ev.currentTarget.focus();
+      pressAtRef.current = performance.now();
+    }
 
     if (kind !== 'move') {
       const bit = BUTTON_MASK[ev.button] ?? 0;
@@ -351,6 +371,10 @@ export const MinesweeperPanel = () => {
           game or a repair for when it stops behaving, and a footer is where neither gets read. */}
       <div className="flex shrink-0 items-center gap-4 text-sm text-primary">
         <span>{connected ? 'connected' : 'connecting…'}</span>
+        {/* Temporary — see `pressAtRef`. ~50ms of this is the game and the capture; the rest is the trip. */}
+        <span title="Press to painted pixels, measured in this browser. Source-side is ~50ms of it.">
+          lag {lagMs === null ? '—' : `${lagMs}ms`}
+        </span>
         {/* Focus decides where keys go, and a canvas gives no hint that it can hold any. */}
         <span>click the board to send it keys</span>
         <button type="button" onClick={() => void refresh()} className="flex items-center gap-1.5 hover:underline">