diff --git a/sfm/event_browser.html b/sfm/event_browser.html
index 357e718..5d7a493 100644
--- a/sfm/event_browser.html
+++ b/sfm/event_browser.html
@@ -629,6 +629,22 @@ function renderWaveform(data) {
       return (Number.isInteger(v) ? String(v) : v.toFixed(1)) + xAxisUnit;
     };
 
+    // Y-axis bounds.  Geophone waveforms render symmetric around zero
+    // (seismograph convention — zero line in the middle, signal goes
+    // up AND down).  Mic + histograms keep default auto-scale (always
+    // positive values; zero at the bottom).
+    let yBounds = {};
+    const isGeoWaveform = !isHistogram && ch !== 'MicL';
+    if (isGeoWaveform) {
+      let absMax = 0;
+      for (const v of values) {
+        const a = Math.abs(v);
+        if (a > absMax) absMax = a;
+      }
+      const padded = (absMax || 1) * 1.10;
+      yBounds = { min: -padded, max: padded };
+    }
+
     const chart = new Chart(canvas, {
       type: isHistogram ? 'bar' : 'line',
       data: {
@@ -677,6 +693,7 @@ function renderWaveform(data) {
             grid: { color: isPrintMode ? '#e0e0e0' : '#21262d', drawTicks: showXAxis },
           },
           y: {
+            ...yBounds,
             ticks: { color: isPrintMode ? '#666' : '#484f58', maxTicksLimit: 5 },
             grid: { color: isPrintMode ? '#e0e0e0' : '#21262d' },
             title: { display: true, text: unit,
diff --git a/sfm/sfm_webapp.html b/sfm/sfm_webapp.html
index e072566..2c4a912 100644
--- a/sfm/sfm_webapp.html
+++ b/sfm/sfm_webapp.html
@@ -2670,6 +2670,24 @@ function _renderScWaveform(data) {
       return String(v) + xAxisLabel;
     };
 
+    // Y-axis bounds.  Convention:
+    //   - Geophones (Tran/Vert/Long) on waveform-mode events:
+    //     symmetric around zero so the zero line sits in the middle and
+    //     positive/negative excursions are visually balanced.
+    //   - Mic (always positive sound pressure) + histograms (per-interval
+    //     peaks, always positive): default auto-scale, zero at the bottom.
+    let yBounds = {};
+    const isGeoWaveform = !isHistogram && ch !== 'MicL';
+    if (isGeoWaveform) {
+      let absMax = 0;
+      for (const v of values) {
+        const a = Math.abs(v);
+        if (a > absMax) absMax = a;
+      }
+      const padded = (absMax || 1) * 1.10;
+      yBounds = { min: -padded, max: padded };
+    }
+
     _scCharts[ch] = new Chart(canvas, {
       type: isHistogram ? 'bar' : 'line',
       data: {
@@ -2709,6 +2727,7 @@ function _renderScWaveform(data) {
             grid:  { color: '#21262d', drawTicks: showX },
           },
           y: {
+            ...yBounds,
             ticks: { color: '#484f58', maxTicksLimit: 4 },
             grid:  { color: '#21262d' },
             title: { display: true, text: chData.unit || '', color: '#484f58', font: { size: 9 } },
@@ -3072,7 +3091,8 @@ if (currentSection === 'db') {
         <h4>Event</h4>
         <dl class="sc-grid">
           <dt>Serial</dt>           <dd id="sc-f-serial">—</dd>
-          <dt>Timestamp</dt>        <dd id="sc-f-ts">—</dd>
+          <dt title="When the seismograph recorded this event (from the BW report's Event Time field)">Recorded at</dt>
+                                    <dd id="sc-f-ts">—</dd>
           <dt>Record type</dt>      <dd id="sc-f-rt">—</dd>
           <dt>Sample rate</dt>      <dd id="sc-f-sr">—</dd>
           <dt>Waveform key</dt>     <dd id="sc-f-key">—</dd>
@@ -3104,7 +3124,8 @@ if (currentSection === 'db') {
           <dt id="sc-l-bwsize">File size</dt>   <dd id="sc-f-bwsize">—</dd>
           <dt id="sc-l-sha">File sha256</dt>    <dd id="sc-f-sha">—</dd>
           <dt>Source kind</dt>      <dd id="sc-f-src">—</dd>
-          <dt>Captured at</dt>      <dd id="sc-f-cap">—</dd>
+          <dt title="When our server received and stored this event (sfm-db insert time, not the recording time)">Received by server at</dt>
+                                    <dd id="sc-f-cap">—</dd>
         </dl>
       </div>
       <div class="sc-section">