static void toggle_tracking_mode(GtkWidget *box,	gpointer   user_data)
{
    ICartesianControl *crt = (ICartesianControl *) user_data;
    bool trck;
    crt->getTrackingMode(&trck);
    if (trck)
        crt->setTrackingMode(false);        
    else
        crt->setTrackingMode(true);        
    return;
}