McNally v. State, 980 A.2d 364 (Del. 2009)

the firearms examiner's inability to recall how he arrived at a conclusion that certain shell castings had similar markings did not render admission of his expert testimony plain error because (1) he explained the principles and methods that he uses when testing casings for identifiable markings (2) the law requires the principle and methods - not the conclusions to be scientifically valid.Thus, we cannot find plain error because Rone did explain his principles and methodology and applied those principles and methods to the facts. McNally was able to cross examine Rone on those principles and his methodology. McNally was also able to expose Rone's lack of recollection about the application of the methodology to the facts here.