52While that assessment of the proportionality of the amount of such a contractual penalty is a matter solely for the national authority before which any dispute is brought, it is nevertheless appropriate, in order to provide a useful response to the referring court, to state that, for the purposes of that assessment, account may be taken, inter alia, of the initial duration of the contract in question, the remaining duration at the time of its termination, the quantity of electricity which was purchased with a view to the performance of that contract but which will not ultimately be consumed by the customer, and the means which a reasonably diligent supplier would have had at its disposal to limit any economic losses that it might incur as a result of that early termination.