Description: According to ISO 17025 and ISO 5725 qualities of tests and qualifying level of laboratory should be confirmed by intralaboratory monitoring. For this purpose it is recommended to use the control cards of Shuharta modified for test process. However application of control cards for "atypical" situations, when there is no direct an exit of results for a test objective level, has no theoretical substantiation and in a greater degree has the heuristic character which is based on intuition of the researcher. In given article results of the analysis of possible situations on which it is possible to judge infringement of conditions of repeatability and (or) reproducibility in test laboratory are spent.
Keywords: Shewhart control chart, Out-Of-Control Process, special causes