Pursuant to s. 258 (1)(c), an accused who wants to rebut the presumption that the blood alcohol readings were accurate and conclusive proof of the accused’s blood alcohol levels at the time the samples were taken requires evidence tending to show that the approved instrument was malfunctioning or was operated improperly. For example, the accused might rely on a maintenance log that shows that the instrument was not maintained properly or on admissions by the technician that there had been erratic results. The accused can request the disclosure of any relevant evidence that is reasonably available in order to be able to present a real defence. It should be noted that the defence created by Parliament is not illusory simply because accused persons will rarely succeed in raising a reasonable doubt that the instrument was functioning or was operated properly.