The Supreme Court of New Jersey ruled in State v Chun that the operators of Alcotest 7110 must wait at least 20 minutes before collecting a sample from a person who has been arrested in order to avoid over estimating the reading due to the possible effects of residual alcohol in the mouth. The machine is programmed to prohibit operation of he device before the passage of 20 minutes from the time entered as the time of arrest.

In addition the operator must observe the test subject for twenty minutes prior to the time of the taking of the test to guarantee that no alcohol has entered the person's mouth while the person is waiting to be tested.

Also if the subject swallows anything or regurgitates or the operator notices chewing gum or tobacco or other foreign objects in the person's mouth, the operator must start the 20 minute period anew.

The person must be observed for 20 minutes. It is not enough that the person be arrested in the back of a police car