What is the standard of review in a section 1538.5 hearing?

"In People v. Lawler (1973) 9 Cal.3d 156, 160 [107 Cal.Rptr. 13, 507 P.2d 621], we expressed the standard to be applied in appellate review of a section 1538.5 hearing: 'In such a proceeding the power to judge the credibility of witnesses, resolve any conflicts in the testimony, weigh the evidence and draw factual inferences, is vested in the trial court. On appeal all presumptions favor the exercise of that power, and the trial court's findings on such matters, whether express or implied, must be upheld if they are supported by substantial evidence. The trial court also has the duty to decide whether, on the facts found, the search was unreasonable within the meaning of the Constitution.... Of course, if ... review is ... sought, it becomes the ultimate responsibility of the appellate court to measure the facts, as found by the trier, against the constitutional standard of reasonableness.' (Italics added.) It follows that section 1538.5 review encompasses a two-step process. We must first determine whether the trial court's findings of fact, implicit or explicit, are supported by substantial evidence. We must then decide whether, in reaching its decision, the trial court properly applied constitutional standards to those facts." (People v. North (1981) 29 Cal.3d 509, 513, 174 Cal.Rptr. 511, 629 P.2d 19.)

a.