(1) Where specification of performance is left to a third party, then in case of doubt it is to be assumed that the specification is to be made at the reasonably exercised discretion of the third party.
(2) If the specification is made by more than one third party, then in case of doubt, the agreement of all parties is necessary; where an amount is to be specified and several amounts are specified, then in case of doubt, the average amount will apply.