The purpose of this International Standard is to define the requirements for demonstrating acceptable performance of safety system instrument channels through response time testing, calibration verification, and other means. The same requirements may be adopted for demonstrating the acceptable performance of non-safety systems and other instrument channels. This Standard contains the main topics in its body and includes annexes to provide further information. The annexes are for information only and contain a selection of the available methods. The methods described in this Standard are used to check instrument calibration for accuracy and time response. It covers direct methods used to set calibration within required tolerances and indirect methods to indicate a need for a direct calibration. The use of the indirect methods allows for longer periods between the routine direct calibrations.