private void OnFactorChanged(ppmmEventArgs e)
 {
     if (FactorChanged != null)
     {
         FactorChanged(e);
     }
 }
    public static void OnFactorChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
    {
        PPMMSingleton ppmm = (PPMMSingleton)sender;
        ppmmEventArgs e    =
            new ppmmEventArgs(
                (double?)args.OldValue,
                (double?)args.NewValue);

        ppmm.OnFactorChanged(e);
    }