This part of IEC 1094 is applicable to working standard microphones It specifies mechanical dimensions and certain electroacoustical characteristics for working standard microphones used in measuring systems for the determination of sound pressure to enable these microphones to be used as transfer standards in the calibration of acoustic measurement instruments. It establishes a system for classifying working standard microphones into a number of types according to their dimensions and properties in order to facilitate the specification of measurement systems, the calibration of measuring systems and microphones by sound calibrators, and the interchangeability of microphones in given measuring and calibration systems. It does not specify the transduction principle by which working standard microphones operate.