Most do not know that only 3 tests have been standardized.

Horizontal Gaze Nystagmus (HGN) and the Walk and Turn

One-leg stand and Finger to Nose instructions

Rhomberg with Recitation test.

Cover of the field "flip-book" issued to all law enforcement

This book is what all law enforcement officer used in their training.  They are familiar with is and most use it each time they do a DUI investigation.  Those officers who claim to have "memorized it" usually do not follow the proper procedures and tend to make up their own.  Any deviation from the standardized instructions can result in the results being biased.