A trial court properly allowed an officer testifying as an expert witness regarding the accuracy of a blood alcohol test device to testify to hearsay statements. The testifying officer was the officer in charge of preliminary alcohol screening (PAS) tests for the department, and he testified regarding tests he had performed to ensure that the PAS device was working properly. He stated that he determined the accuracy of the device by using a test solution provided by the manufacturer that had a known alcohol content of .10 percent, which he determined by reading the label on the test solution. Defendant objected that this was hearsay, but was overruled by the trial court. The appellate court affirmed, noting that an expert witness may base his opinion on hearsay. Although the officer was not expressly declared an expert witness by the court, the record made it clear that all parties understood that he was testifying as an expert. Finally, under People v. Williams (2002) 28 Cal.4th 408, deficiencies in the manner of testing went to the weight of the evidence, not to its admissibility.