IEC 60942:2003

Specifies the performance requirements for three classes of sound calibrator: laboratory standard (class LS), class 1 and class 2. Tolerance limits are smallest for class LS and greatest for class 2  instruments. Class LS sound calibrators are normally used only in the laboratory; class 1 and class 2 are considered as sound calibrators for field use. A class 1 sound calibrator is primarily intended for use with a class 1 sound level meter and a class 2 sound calibrator primarily with a class 2 sound level meter, as specified in IEC 61672-1.
The tolerance limits for class LS sound calibrators are based on the use of a laboratory standard microphone, as specified in IEC 61094-1, for demonstrations of conformance to the requirements of this standard. The tolerance limits for class 1 and class 2 sound calibrators are based on the use of a working standard microphone, as specified in IEC 61094-4, for demonstrations of conformance to the requirements of this standard.
This third edition cancels and replaces the second edition published in 1997, and its amendment 1 (2000), of which it constitutes a technical revision.