Which of the following is NOT one of the six clues observed during the HGN exercise?

The clue that is not part of the Horizontal Gaze Nystagmus (HGN) exercise is blurred vision while stationary. The HGN test is designed to assess the presence of nystagmus, which is an involuntary eye movement that can indicate impairment due to alcohol or drugs. The six specific clues involved in the HGN test include the onset of nystagmus at or before 45 degrees, lack of smooth pursuit, and distinct and sustained nystagmus at maximum deviation, which are all direct observations of eye movements in relation to a stimulus.

Blurred vision while stationary does not relate to the specific eye movements being evaluated in the HGN exercise and therefore does not fit within the recognized clues used by law enforcement officers during this sobriety test. By focusing on the specific indicators of nystagmus, officers can more accurately assess impairment.