diff --git a/lang/en/tool_excimer.php b/lang/en/tool_excimer.php
index 0b778be..b8e718c 100644
--- a/lang/en/tool_excimer.php
+++ b/lang/en/tool_excimer.php
@@ -79,6 +79,7 @@
 $string['field_finished'] = 'Finished';
 $string['field_fuzzycount'] = 'Approx. count';
 $string['field_fuzzydurationcounts'] = 'Histogram';
+$string['field_estimatedduration'] = 'Est. duration (s)';
 $string['field_fuzzydurationsum'] = 'Approx. total duration (s)';
 $string['field_hostname'] = 'Host name';
 $string['field_id'] = 'ID';
diff --git a/page_group.php b/page_group.php
index 05dd74f..d4fc99a 100644
--- a/page_group.php
+++ b/page_group.php
@@ -23,7 +23,7 @@
  * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
-use core\chart_line;
+use core\chart_bar;
 use core\chart_series;
 use tool_excimer\helper;
 use tool_excimer\monthint;
@@ -57,6 +57,11 @@
 $data->approxcount = pow(2, $data->fuzzycount - 1) . ' - ' . pow(2, $data->fuzzycount);
 $data->approxduration = pow(2, $data->fuzzydurationsum);
 $data->histogram = helper::make_histogram($data);
+// Add estimated duration (count × upper bound) to each histogram row.
+foreach ($data->histogram as &$row) {
+    $row['duration'] = $row['value'] * $row['high'];
+}
+unset($row);
 
 // Data for charts.
 // Each duration range forms its own line on the chart.
@@ -101,21 +106,56 @@
     for ($rangeindex = 0; $rangeindex < $highest; ++$rangeindex) {
         $value = 0;
         if (isset($histograms[$month][$rangeindex])) {
-            $value = $histograms[$month][$rangeindex]['value'];
-            $linelabels[$rangeindex] = get_string('fuzzydurationrange', 'tool_excimer', $histograms[$month][$rangeindex]);
+            $entry = $histograms[$month][$rangeindex];
+            // Weight count by upper bound of duration range to represent total seconds.
+            $value = $entry['value'] * $entry['high'];
+            $linelabels[$rangeindex] = get_string('fuzzydurationrange', 'tool_excimer', $entry);
         }
         $durationseries[$rangeindex][] = $value;
     }
     $month = monthint::increment_month($month);
 }
 
-$chart = new chart_line();
+$chart = new chart_bar();
+$chart->set_stacked(true);
 $chart->set_labels($labels);
 
+// Colour stops from green to yellow to orange to red to purple.
+$colorstops = [
+    [0x2ecc71, 0], // Green.
+    [0xf1c40f, 25], // Yellow.
+    [0xe67e22, 50], // Orange.
+    [0xe74c3c, 75], // Red.
+    [0x8e44ad, 100], // Purple.
+];
+
+// Interpolate a hex colour along the defined stops given a 0-100 position.
+$interpolatecolor = function (float $pct) use ($colorstops): string {
+    for ($i = 0; $i < count($colorstops) - 1; $i++) {
+        [$cola, $posa] = $colorstops[$i];
+        [$colb, $posb] = $colorstops[$i + 1];
+        if ($pct <= $posb) {
+            $t = ($posb === $posa) ? 0 : ($pct - $posa) / ($posb - $posa);
+            $r = (int) round((($cola >> 16) & 0xff) * (1 - $t) + (($colb >> 16) & 0xff) * $t);
+            $g = (int) round((($cola >> 8) & 0xff) * (1 - $t) + (($colb >> 8) & 0xff) * $t);
+            $b = (int) round(($cola & 0xff) * (1 - $t) + ($colb & 0xff) * $t);
+            return sprintf('#%02x%02x%02x', $r, $g, $b);
+        }
+    }
+    [$lastcol] = end($colorstops);
+    return sprintf('#%02x%02x%02x', ($lastcol >> 16) & 0xff, ($lastcol >> 8) & 0xff, $lastcol & 0xff);
+};
+
 // Add each duration range to the chart, but only those that have non-zero counts.
 foreach ($durationseries as $idx => $series) {
     if (max($series) != 0) {
-        $chart->add_series(new chart_series($linelabels[$idx], $series));
+        // Map colour by log base 16 of duration: each factor of 16 = one colour stop.
+        // idx is the duration exponent (high = 2^idx), so 4 idx steps = factor of 16.
+        // Colour stops: idx 0 = green, 4 = yellow, 8 = orange, 12 = red, 16+ = purple.
+        $pct = min(100.0, $idx * 100.0 / 16.0);
+        $s = new chart_series($linelabels[$idx], $series);
+        $s->set_color($interpolatecolor($pct));
+        $chart->add_series($s);
     }
 }
 
diff --git a/templates/page_group.mustache b/templates/page_group.mustache
index 63925d9..b3350f8 100644
--- a/templates/page_group.mustache
+++ b/templates/page_group.mustache
@@ -49,7 +49,7 @@
 <div id="profile-stats" class="container">
     <div class="row">
         <div>
-            <table class="flexible table table-striped table-sm table-hover generaltable generalbox w-auto">
+            <table class="table table-striped table-sm table-hover w-auto">
                 <tr>
                     <th>{{#str}}field_month, tool_excimer{{/str}}</th>
                     <td>{{month}}</td>
@@ -65,15 +65,17 @@
             </table>
         </div>
         <div>
-            <table class="flexible table table-striped table-sm table-hover generaltable generalbox w-auto">
+            <table class="table table-striped table-sm table-hover w-auto">
                 <tr>
                     <th>{{#str}}field_fuzzydurationcounts, tool_excimer{{/str}}</th>
                     <td></td>
+                    <th>{{#str}}field_estimatedduration, tool_excimer{{/str}}</th>
                 </tr>
                 {{#histogram}}
                     <tr>
                         <td>{{low}} - {{high}}s</td>
                         <td>{{value}}</td>
+                        <td>{{duration}}s</td>
                     </tr>
                 {{/histogram}}
             </table>
diff --git a/version.php b/version.php
index a20831f..e82db44 100644
--- a/version.php
+++ b/version.php
@@ -25,8 +25,8 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version = 2026031703;
-$plugin->release = 2026031703;
+$plugin->version = 2026031704;
+$plugin->release = 2026031704;
 $plugin->requires  = 2023100900; // Moodle 4.3.
 $plugin->supported = [403, 405];
 $plugin->component = 'tool_excimer';