What is the degree threshold prior to which nystagmus onset is considered a clue in the HGN test?

The degree threshold prior to which nystagmus onset is considered a clue in the Horizontal Gaze Nystagmus (HGN) test is 45 degrees. This means that if nystagmus is observed when the eye is moved to an angle greater than 45 degrees from center, it is an indicator that could suggest impairment due to alcohol or other substances. In law enforcement training for conducting HGN tests, a consistent understanding of these thresholds is crucial as they help in assessing a person's level of impairment effectively. Recognizing nystagmus onset at this specific angle adds credibility to the observation and supports the case for further evaluation of the individual's sobriety or impairment level.