An accumulator option in which the payoff depends on the spot price being above or below the predetermined trigger. Each time the trigger is reached on a fixing date, the notional decreases, i.e., it is deducted by a specific proportion.

This option is based on the purchase (sale) of a knock-out one-sided call (put) option and the sale (purchase) of knock-out one-sided put (call) option, all having the same strike (forward rate), fixing dates, and expiration date.