diff --git a/inc/myco_objects.js b/inc/myco_objects.js
index ef1c1d1..a8ee650 100644
--- a/inc/myco_objects.js
+++ b/inc/myco_objects.js
@@ -1,10 +1,13 @@
 function GroupList() {
+
+  lastChange=0;
   
   this.loadFromLocalStorage=function() {
     if (localStorage.groups!==undefined) {
-      var groups=JSON.parse(localStorage.groups);
-      for (el in groups) {
-        this[el]=new Group(el,groups[el]);
+      var data=JSON.parse(localStorage.groups);
+      this.lastChange=data.lastChange;
+      for (el in data.groups) {
+        this[el]=new Group(el,data.groups[el]);
       }
     }
   }
@@ -20,7 +23,10 @@ function GroupList() {
   }
 
   this.save=function() {
-    localStorage.groups=JSON.stringify(this.export());
+    localStorage.groups=JSON.stringify({
+      'lastChange': new Date().getTime(),
+      'groups': this.export()
+    });
   }
 
   this.each=function(fct) {
@@ -174,7 +180,8 @@ function Group(name,data) {
             data.contributions[idx].cost,
             data.contributions[idx].title,
             data.contributions[idx].date,
-            idx
+            idx,
+            data.contributions[idx].lastChange
           ));
         }
       }
@@ -198,18 +205,20 @@ function Contributor(name,email,id) {
   }
 }
 
-function Contribution(contributor,cost,title,date,id) {
+function Contribution(contributor,cost,title,date,id,lastChange) {
   this.contributor=contributor;
   this.cost=cost;
   this.title=title;
   this.date=date;
   this.id=id;
+  this.lastChange=lastChange || new Date().getTime();
   this.export=function() {
     return {
       'contributor': this.contributor.name,
       'cost': this.cost,
       'title': this.title,
       'date': this.date,
+      'lastChange': this.lastChange,
     };
   }