Charles A. answered • 05/10/19
Vassar/UCLA Law-Educated Legal Tutor Specializing in 1L Curriculum
This is generally a two-step process. The officer testifies to the manner in which the breath analysis took place (instructions he or she gave, what the defendant did in response, etc.) and then states what results the machine produced. Typically the suspect blows twice, and produces two readings that have to be relatively close in agreement; otherwise the machine requires a third sample. However, the state must also prove that the machine was properly functioning and calibrated. This testimony comes from a criminalist or other scientific employee who maintains the machine. They introduce maintenance and calibration records, as well as historical machine results which include the suspect's breath test. To the extent a defense attorney believes the machine was improperly maintained or calibrated, it is possible to challenge the admission of the test results in a pre-trial motion, before the jury hears the results. If the judge does not allow that, the issue might have to be litigated in front of the jury, with both sides arguing their respective positions on the test's accuracy. Generally, though, the machines are well-maintained and excluding the results from evidence relatively difficult.
