The NHTSA manual requires three parts to the HGN or Horizontal Gaze Nystagmus test. Most people refer to this test as the "pen test" or "eye test." The officer is holding some sort of pen or light in front of your eyes and passing it back and forth to look for clues of intoxication.
First, the officer must advise the suspect to remove any glasses and then to stand with the feet together and arms by their side. The person should then be told that they are to hold their head still because they are going to be required to follow the path of the light or pen with their eyes only. If they fail to follow that instruction, then the police officer is supposed to note that in their report as a clue that the individual has lost the normal use of their mental faculties because they cannot follow instructions and they are DWI.
The object should be moved from side to side about 12 inches from the suspect's eyes. The officer should make a quick pass on each eye to ensure equal tracking. This portion of the HGN field sobriety test should only take 2 seconds.