This part of IEC 60645 applies to instruments designed primarily for the measurement of otoacoustic emissions in the human external auditory meatus evoked by acoustic probe stimuli. This standard defines the characteristics to be specified by the manufacturer, provides performance specifications for two types of instruments1 and specifies the functions to be provided by these types. This part of IEC 60645 describes methods to be used for approval testing and guidance on methods for periodic calibration. The purpose of this part of IEC 60645 is to ensure that measurements made under comparable test conditions with different instruments complying with the standard will be consistent. Instruments which provide a measurement function not specifically within the scope of the standard shall still comply with any relevant requirements. This document is not intended to restrict development or incorporation of new features, nor to discourage innovative approaches.