This description of the Walk and Turn test posted by San Francisco DUI Lawyer.

A second scoring factor is known as starting too soon. This is given when the starts to walk before the officer instructs them to do so. This can only be scored if the officer specifically instructed the suspect not to start until told to begin and the suspect stated they understood this instruction.

The second stage of this test is known as the Walking Stage. The suspect is informed again that when he is told to start, they must take nine heel to toe steps down the line, turn around, and take nine heel to toe steps back. The officer must demonstrate two or three heel to toe steps for the suspect. The officer then informs the suspect and demonstrates how and when the turn is to be executed. They are shown to keep the foot on the line, and turn by taking a series of small steps. If the officer demonstrates or instructs with the incorrect foot the suspects turn may be affected and incorrectly scored. This is also known as "wrong footing". The officer informs the suspect to keep their arms at their sides while walking, watch their feet at all times, and to count their steps out loud. They must be advised not to stop once they start walking and not until they complete the test. If the officer does not receive an affirmative response of understanding the test may not be scored fairly and properly, thereby invalidating the results. 

The maximum score obtained on this test is eight. There are six scoring factors that can be observed in the walking stage. The first one is stopping while walking to steady themselves. The officer can not score this item if the suspect is merely walking too slow. The suspect must pause for several seconds after one step. If this occurs, the officer is trained to have the suspect begin from the point of difficulty instead of starting over. This test loses sensitivity if repeated several times. The next scoring factor is not touching heel to toe. The suspect must leave a one half inch or more space between the heel and toe on any step. This is only scored once no matter how many times it appears. The feet do not have to actually touch on these steps.