When the future or the forward comprises a range of deliverable instruments, offsetting of positions in the futures or forward contract and its underlying is only permitted in cases where there is a readily identifiable underlying security which is most profitable for the trader with a short position to deliver. The price of this security, sometimes called the "cheapest-to-deliver", and the price of the future or forward contract must, in such cases, move in close alignment. No offsetting is allowed between positions in different currencies. The separate legs of cross-currency swaps or forward foreign exchange contracts are treated as notional positions in the relevant instruments and included in the appropriate calculation for each currency.