This part of IEC 61672 describes procedures for periodic testing of time-weighting, integrating-averaging, and integrating sound level meters that were designed to the class 1 or class 2 requirements of IEC 61672-1. The aim of the standard is to ensure that periodic testing is performed in a consistent manner by all calibration laboratories. The purpose of periodic testing is to assure the user that the performance of a sound level meter conforms to the applicable requirements of IEC 61672 1 for a limited set of key tests and for the environmental conditions under which the tests were performed. The extent of the tests in this part of IEC 61672 is deliberately restricted to the minimum considered necessary for periodic tests. Periodic tests described in this part of IEC 61672 apply to sound level meters for which the model has been, or has not been, pattern approved by an independent testing organization responsible for pattern approvals and in accordance with the test procedures of IEC 61672 2. Periodic tests described in this part of IEC 61672 also apply to sound level meters for which the manufacturer claims conformance to the requirements of IEC 61672 1. Because of the limited extent of the periodic tests, if evidence of pattern approval is not publicly available no general conclusion about conformance to the requirements of IEC 61672 1 can be made, even if the results of the periodic tests conform to all applicable requirements of this part of IEC 61672.