diff --git a/index.html b/index.html
index d23dcfc..f51a49e 100644
--- a/index.html
+++ b/index.html
@@ -153,8 +153,9 @@ distance = TOF · c    avec  c ≈ 1500 m/s en eau de mer
   <div style="margin-top:10px;" class="legend">
     <span><span class="sw" style="background:#5ad1ff"></span>USBL A (fixe)</span>
     <span><span class="sw" style="background:#ff8b5a"></span>USBL B (mobile)</span>
-    <span><span class="sw" style="background:#5ad1ff"></span>ping (A→B)</span>
-    <span><span class="sw" style="background:#ff8b5a"></span>pong (B→A)</span>
+    <span><span class="sw" style="background:#5ad1ff"></span>ping1 (A→B, plein)</span>
+    <span><span class="sw" style="background:#ff8b5a"></span>pong (B→A, plein)</span>
+    <span><span class="sw" style="background:transparent;border:2px solid #5ad1ff;border-radius:2px"></span>ping2 (A→B, anneau)</span>
   </div>
   <canvas id="plot" width="900" height="220" style="margin-top:14px;"></canvas>
   <div class="legend" style="margin-top:6px;">
@@ -338,8 +339,13 @@ Ce schéma est exactement celui qu'utilisent les puces UWB <b>DecaWave DW1000 /
   const history = [];
   let nCycles = 0;
 
+  // Guard interval (s sim) between two consecutive cycles, to avoid the visual
+  // confusion where A's ping2 (end of cycle N) and ping1 (start of cycle N+1)
+  // look like two back-to-back transmissions from A.
+  const CYCLE_GUARD = 0.6;
+
   function ensureCycle() {
-    if (!cycle || simT >= cycle.tPing2Recv) {
+    if (!cycle || simT >= cycle.tPing2Recv + CYCLE_GUARD) {
       if (cycle) {
         history.push({
           tStart: cycle.tPing1Send,
@@ -352,7 +358,7 @@ Ce schéma est exactement celui qu'utilisent les puces UWB <b>DecaWave DW1000 /
         nCycles++;
         if (history.length > 600) history.shift();
       }
-      const startT = cycle ? cycle.tPing2Recv : 0;
+      const startT = cycle ? cycle.tPing2Recv + CYCLE_GUARD : 0;
       cycle = buildCycle(startT);
     }
   }
@@ -405,9 +411,9 @@ Ce schéma est exactement celui qu'utilisent les puces UWB <b>DecaWave DW1000 /
     // Pulses for current cycle
     if (cycle) {
       const pulses = [
-        { sendT: cycle.tPing1Send, recvT: cycle.tPing1Recv, fromA: true,  color: '#5ad1ff', label: 'ping' },
-        { sendT: cycle.tPongSend,  recvT: cycle.tPongRecv,  fromA: false, color: '#ff8b5a', label: 'pong' },
-        { sendT: cycle.tPing2Send, recvT: cycle.tPing2Recv, fromA: true,  color: '#5ad1ff', label: 'ping2' },
+        { sendT: cycle.tPing1Send, recvT: cycle.tPing1Recv, fromA: true,  color: '#5ad1ff', label: 'ping1', shape: 'solid' },
+        { sendT: cycle.tPongSend,  recvT: cycle.tPongRecv,  fromA: false, color: '#ff8b5a', label: 'pong',  shape: 'solid' },
+        { sendT: cycle.tPing2Send, recvT: cycle.tPing2Recv, fromA: true,  color: '#5ad1ff', label: 'ping2', shape: 'ring' },
       ];
       for (const p of pulses) {
         if (t < p.sendT || t > p.recvT) continue;
@@ -421,8 +427,14 @@ Ce schéma est exactement celui qu'utilisent les puces UWB <b>DecaWave DW1000 /
         const x = xs + (xe - xs) * frac;
         ctx.beginPath();
         ctx.arc(x, yLine, 7, 0, Math.PI * 2);
-        ctx.fillStyle = p.color;
-        ctx.fill();
+        if (p.shape === 'ring') {
+          ctx.strokeStyle = p.color;
+          ctx.lineWidth = 2.5;
+          ctx.stroke();
+        } else {
+          ctx.fillStyle = p.color;
+          ctx.fill();
+        }
         // trail
         const trailLen = 60;
         const dir = (xe > xs) ? -1 : 1;