A contractual expert determination arises where the parties entrust one or more persons, chosen for their particular technical expertise, with the task of making a technical finding which they undertake to accept as a direct expression of their contractual intention, and it constitutes a source of supplementation of the contract. A contractual expert determination differs from arbitraggio because the arbitrator-expert must not be guided by the search for an economic balance according to a criterion of commercial fairness, but must adhere to technical rules and to the technical and scientific criteria proper to the discipline within which the assessment entrusted to him falls. A contractual expert determination does not confer the task of resolving disputes which have arisen or may arise between the parties in relation to the legal relationship, but merely that of formulating a technical appraisal which they undertake to accept, the determination remaining open to challenge only for mistake, fraud, duress and incapacity of the parties.