In Neudeck v. Bransten (1965) 233 Cal.App.2d 17, 19, the court held that a professor of mechanical engineering and author of a book on the laws of physics as applied to billiard balls, was not qualified to testify in an auto collision case because there was no showing that he had any actual experience investigating traffic accidents. Similarly, in Pearce v. Linde (1952) 113 Cal.App.2d 627, the court held that a medical expert was not qualified as a witness unless it could be shown that he was familiar with the standards required of physicians under similar circumstances. the court said that it was practical knowledge of what is usually done by physicians under circumstances similar to those that confronted the defendant that was important in determining the competency of the expert to testify as to the degree of care required. (Id. at pp. 629-631.) Finally, in Miller v. Los Angeles County Flood Control Dist. (1973) 8 Cal.3d 689, the court affirmed the exclusion of an expert who was to testify about whether a reasonably prudent builder would have used a retaining wall to prevent flooding that damaged a home. the excluded expert in Miller was a mechanical engineer trained in hydraulics and was familiar with flooding in hillside areas; however, he had no experience constructing homes and admitted he was unfamiliar with building practices. (Id. at p. 701.)