Provides guidance in choosing procedures and determining parameters used to select and validate methods of chemical analysis through the determination of the precision of those methods. Precision is determined in terms of repeatability, within-laboratory reproducibility and reproducibility. Defines relevant statistical terms, specifies test material requirements and discusses the number of laboratories required as well as the functions of a 'steering' committee to coordinate activities. Includes computer program to calculate repeatability and reproducibility and four samples of results sheets. Applicable to laboratories reasonably experienced in the methods to be evaluated with respect to the materials being analyzed.