1.1 This standard describes the criterion to be used for selection of a WRM and procedures to be used for determining within lab and between lab tolerances of changes in measured properties of a reference material intended for use in monitoring operating conditions to establish the consistency of exposure tests. Note 1 -Examples of laboratory accelerated tests in which a weathering reference material could be used to monitor consistency are light and water exposure tests such as those described in Practices G 152, G 153, and G 154 G 155and other standards in which tests conducted according to these standards are referenced. Examples of outdoor exposures where a weathering reference material could be used to monitor consistency are those conducted according to Practices G 7, G 24, or G 90. A reference material can also be used to monitor consistency of exposure or conditioning test that do not involve exposure to light. 1.2 This practice does not cover (1) control materials used for comparison of stability with test materials, or (2) standard materials used to time exposures. 1.3 This practice provides an outline of experiments required to determine how the measured properties of the reference material change as a function of exposure to specified test conditions. It includes establishment of reproducible measurement procedures, determination of the critical region in the light source causing the changes, and effects of other critical exposure stresses such as temperature and moisture. 1.4 This practice describes procedures for conducting round-robin tests with the weathering reference material to determine reproducibility of the reference material property change in exposures conducted in different laboratories, and the repeatability when replicate reference material specimens are exposed in a single device and tested in one laboratory. 1.5 This practice describes procedures for using the results from analysis of variance on results from round-robin tests to determine the contribution of the exposure, the measurement device, reference material variability, and operator error to total variability.