void UnsubscribeEvents(ITicker prev)
 {
     prev.OrderBook.OnChanged -= OnTickerOrderBookChanged;
     prev.Changed             -= OnTickerChanged;
     prev.HistoryItemAdd      -= OnTickerHistoryItemAdded;
     prev.TradeHistoryAdd     -= OnTickerTradeHistoryAdd;
     prev.UnsubscribeOrderBookUpdates();
     prev.UnsubscribeTickerUpdates();
     prev.UnsubscribeTradeUpdates();
 }