What constitutes substantial evidence in a motion to overturn a finding of not guilty?

Appellants argue the trial court's decision is not supported by substantial evidence. As they note, '"[s]ubstantial evidence . . . is not synonymous with "any" evidence.' Instead, it is ""substantial' proof of the essentials which the law requires."' [Citations.] The focus is on the quality, rather than the quantity, of the evidence. 'Very little solid evidence may be "substantial," while a lot of extremely weak evidence might be "insubstantial."' [Citation.] Inferences may constitute substantial evidence, but they must be the product of logic and reason. Speculation or conjecture alone is not substantial evidence. [Citations.] Expert opinion testimony constitutes substantial evidence only if based on conclusions or assumptions supported by evidence in the record. Opinion testimony which is conjectural or speculative 'cannot rise to the dignity of substantial evidence.' [Citation.]" (Roddenberry v. Roddenberry (1996) 44

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