What is the test for determining whether there is a "certainty" over the amount of damages awarded at trial?

Generally, "a determination is one of ultimate fact if it can be reached by logical reasoning from the evidence, but one of law if it can be reached only by the application of legal principles. [Citations.]" (Board of Education v. Jack M. (1977) 19 Cal.3d 691, 698, fn. 3, 139 Cal.Rptr. 700, 566 P.2d 602.) The question before this court would appear to be one of law. The evidence on the issue of the "certainty" of damages was essentially undisputed at trial. Thus, it is necessary to apply legal principles in order to determine if pretrial interest should have been awarded.