In a DUI trial, expert testimony may be admissible as relevant in both “per se DUI” and generic DUI offenses to challenge the validity of the design of the breath test device, its operation, and sampling method. At trial for driving under the influence, defendant attempted to introduce the testimony of an expert challenging the reliability of breath test devices to rebut the presumption of intoxication. The trial court disallowed the testimony stating that the breath test result could not be rebutted in any fashion, for either the “per se” or generic DUI offenses. The appellate court here disagreed, finding that the court was mistaken in stating that the proffered expert testimony was irrelevant; it should have been allowed to be considered as going to the weight to be accorded the test results and did not address partition ratio issues. (See People v. McNeal (2009) 46 Cal.4th 1183, 1199.)