diff --git a/scripts/logviewer/main.js b/scripts/logviewer/main.js
index af5f562c..56d7024e 100644
--- a/scripts/logviewer/main.js
+++ b/scripts/logviewer/main.js
@@ -147,7 +147,7 @@ async function loadFile() {
     logs.items.sort((a, b) => itemStart(a) - itemStart(b));
     rootItem = {c: logs.items};
     itemByRef = new Map();
-    preprocessRecursively(rootItem, itemByRef, []);
+    preprocessRecursively(rootItem, null, itemByRef, []);
 
     const fragment = logs.items.reduce((fragment, item, i, items) => {
         const prevItem = i === 0 ? null : items[i - 1];
@@ -160,7 +160,8 @@ async function loadFile() {
     main.replaceChildren(fragment);
 }
 
-function preprocessRecursively(item, refsMap, path) {
+function preprocessRecursively(item, parentElement, refsMap, path) {
+    item.s = (parentElement?.s || 0) + item.s;
     if (itemRefSource(item)) {
         refsMap.set(itemRefSource(item), item);
     }
@@ -170,7 +171,7 @@ function preprocessRecursively(item, refsMap, path) {
             const child = itemChildren(item)[i];
             const childPath = path.concat(i);
             child.id = childPath.join("/");
-            preprocessRecursively(child, refsMap, childPath);
+            preprocessRecursively(child, item, refsMap, childPath);
         }
     }
 }
diff --git a/src/logging/LogItem.js b/src/logging/LogItem.js
index e699a4ac..cddcfecf 100644
--- a/src/logging/LogItem.js
+++ b/src/logging/LogItem.js
@@ -100,7 +100,7 @@ export class LogItem {
         }
     }
 
-    serialize(filter) {
+    serialize(filter, parentStartTime = null) {
         if (this._filterCreator) {
             try {
                 filter = this._filterCreator(new LogFilter(filter), this);
@@ -111,7 +111,7 @@ export class LogItem {
         let children;
         if (this._children !== null) {
             children = this._children.reduce((array, c) => {
-                const s = c.serialize(filter);
+                const s = c.serialize(filter, this._start);
                 if (s) {
                     if (array === null) {
                         array = [];
@@ -127,7 +127,7 @@ export class LogItem {
         // in (v)alues, (l)abel and (t)ype are also reserved.
         const item = {
             // (s)tart
-            s: this._start,
+            s: parentStartTime === null ? this._start : this._start - parentStartTime,
             // (d)uration
             d: this.duration,
             // (v)alues