We review a court's findings of fact to determine if they are supported by substantial evidence. We have defined "substantial evidence" as consisting of "more than a mere scintilla of evidence but may be somewhat less than a preponderance." Furthermore, "where the findings are based on conflicting evidence, the Court's function is to determine whether there is substantial evidence to support the findings and not to determine whether there is sufficient evidence to support contrary findings." We will not substitute our judgment for that of a trial court when the issue concerns the weight given to certain evidence or the credibility of witnesses. Walls v. Travelers Indem. Co., 281 Mont. 106, 110-11, 931 P.2d 712, 715 (1997) (citations omitted).