In Costello v. Fazio, 256 F.2d 903 (9th Cir. 1958), the court noted the greater area for review when credibility was not in question: 'Where a finding of fact by the referee is based upon conflicting evidence, or where the credibility of witnesses is a factor, a district court and, on appeal, a court of appeals will seldom hold such a finding clearly erroneous. The same reluctance is not encountered with regard to a factual conclusion from given facts. In the latter case, the proper conclusion from given facts can be made by the trial judge, or the court of appeals, as well as the referee.' Id. at 908. Yet, in reversing the decision of the referee, the court in Fazio chose to do so only by holding the finding of the referee 'clearly erroneous.' The Fazio rule was somewhat amplified and the extent of judicial restraint was articulated in the case of Hoppe v. Rittenhouse, 279 F.2d 3, 9 (9th Cir. 1960): 'The rule applied in Fazio is pertinent where the primary facts can fairly be said to admit of but one reasonable conclusion, and yet this principle does not change the equally settled rule that where the basic and undisputed facts are fairly susceptible of diverse inferences requiring different conclusions, the determination made by the trier of fact is conclusive on review unless that finding is 'clearly erroneous'.'