4.1 This guide recommends the use of statistical x-charts to graphically monitor test data determined for the ASTM reference blacks for those test methods given in Section 2. All laboratories are encouraged to utilize statistical x-charts and ASTM reference blacks because this enables a comparison of testing precision within and between laboratories. The guide describes practices for the use of repeatability and reproducibility limits and x-charts.

4.2 In addition to the calibration of a test method by physicochemical means, a statistical method for achieving calibration of a test method is presented (that is, normalization).

4.3 Poor test precision can be the result of poor repeatability or poor reproducibility or both. Causes may include inadequate operator training, improperly maintained equipment or laboratory environment, variation in sample preparation or analysis techniques, the lack of calibration or standardization of instrumentation, worn-out apparatus, reagents that do not meet specifications, different sources of instrumentation or equipment, and material heterogeneity. The sum of all sources of testing error is unique for an individual laboratory.

4.4 Precision data for ASTM Reference Blacks are found in Tables 1-3. These include standard reference blacks (SRB’s) Series 8, HT and INR Iodine Standards. The HT or INR Iodine standards are recommended for monitoring iodine testing.

Note 1: Preferred precision values are bolded in Tables 1-3.

1.1 This guide covers procedures for using the ASTM Standard Reference Blacks2 (SRBs) and the HT and INR Iodine Number Standards to continuously monitor the precision of those carbon black test methods for which reference values have been established. It also offers guidelines for troubleshooting various test methods.

1.2 This guide establishes procedures for the use of x-charts to continuously monitor those tests listed in Section 2 for within-lab precision (repeatability) and between-lab accuracy (reproducibility).

1.3 This guide provides a statistical procedure for improving test reproducibility when a laboratory cannot physically calibrate its apparatus to obtain the reference values of the ASTM reference blacks, within the ranges given in this guide.