(57)For the purposes of Article 19(4) of Directive 2004/39/EC, a transaction may be unsuitable for the client or potential client because of the risks of the financial instruments involved, the type of transaction, the characteristics of the order or the frequency of the trading. A series of transactions that are each suitable when viewed in isolation may be unsuitable if the recommendation or the decisions to trade are made with a frequency that is not in the best interests of the client. In the case of portfolio management, a transaction might also be unsuitable if it would result in an unsuitable portfolio.