Knowing what the 45 degree angle is of critical importance to the proper administration of an HGN test. An officer who cannot accurately visualize and understand what that angle is in relation to your client is a witness who will help defense counsel suppress HGN evidence. According to NHTSA protocol, officers in their training had to be able to accurately determine a 45 degree angle in their administration of the test because taking their stimulus beyond that point will induce nystagmus.
The HGN measuring trial graphics board can be used during cross-examination of the HGN testing officer to determine whether he can accurately measure 45 degrees. The board is presented to the officer upside down (the printing facing the ground) with the middle of the rounded side at the officer's nose and the flat side where your client's nose would have been during the officer's test. The officer is then asked use his finger and touch the edge of the rounded sides where the 45 degree angles would be from your client's nose. You will then mark those spots on the paper provided with your graphics and flip the chart over so that the jury can see how accurate, or more importantly, how inaccurate the officer was in his estimation. Any error by the officer will work to your client's benefit. Further, any error beyond 45 degrees may make the test evidence inadmissible.
Please be careful not to allow the officer to mark your graphics because it might clue the next officer where the correct 45 degree angles do lie. Note, this trial graphic board cannot be generally used twice on the same officer because, like all human beings, they learn from their mistakes.