ISO 389-1:2017 specifies a standard reference zero for the scale of hearing threshold level applicable to pure-tone air conduction audiometers, to promote agreement and uniformity in the expression of hearing threshold level measurements throughout the world.
ISO 389-1:2017 states the information in a form suitable for direct application to the calibration of audiometers, that is, in terms of the reference equivalent threshold sound pressure levels of generic supra-aural earphones specified in 4.2, measured on an ear simulator complying with IEC 60318‑1 and in terms of model-specific data given in two additional tables for the IEC 60318‑3 acoustic coupler and the IEC 60318‑1 ear simulator, respectively.