This part of IEC 60118 specifies methods for measurement of the bone conduction hearing aids characteristics. The methods described will produce a suitable basis for the exchange of information or for direct comparison of the electroacoustical characteristics of bone conduction hearing aids. These methods are chosen to be practical and reproducible and are based on selected fixed parameters. The results obtained by the methods specified in this standard express the performance under the conditions of the measurement but will not necessarily agree exactly with the performance of the hearing aid under practical conditions of use. This document defines methods of measurement of characteristics of bone conduction hearing aids both: " transcutaneously coupled devices measured on a mechanical coupler, meeting requirements of IEC 60318-6, " bone coupled/bone anchored devices measured on a mechanical coupler configured as a skull simulator. NOTE 1 A skull simulator is a mechanical coupler designed to present a specific mechanical impedance to a vibrator coupled with a mechanical coupling Though the number of measurements covered by this part of IEC 60118 is limited, it is not intended that all measurements described herein are mandatory. NOTE 2 Throughout this document all sound pressure levels specified are referred to 20 ¼Pa. When appropriate, sound pressure level will be abbreviated to SPL.