If you modify the values in the table the chart is not updated

I have discussed this behavior with our developers. Chart drawing is a more resource-intensive operation than updating a text in DataGrid cells. So, we do not update the Chart control automatically when you edit an element of the collection, for performance reasons. You can update your Chart manually by using the UpdateData() method.
Alternatively, you can accomplish this task at the level of the ObservableCollection. Handle the PropertyChanged event of the collection items to call the OnCollectionChanged method:

C#
internal class A : ObservableCollection<FinancialPoint>  
   {  
       protected override void InsertItem(int index, FinancialPoint item)  
       {  
           base.InsertItem(index, item);  
           ((INotifyPropertyChanged)item).PropertyChanged += new PropertyChangedEventHandler(A_PropertyChanged);  
       }  
       protected override void RemoveItem(int index)  
       {  
           ((INotifyPropertyChanged)this[index]).PropertyChanged -= new PropertyChangedEventHandler(A_PropertyChanged);  
           base.RemoveItem(index);  
       }  
       void A_PropertyChanged(object sender, PropertyChangedEventArgs e)  
       {  
           OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset, null));  
       }  
   }