1.1 This practice defines means for describing system performance (ex vivo) and, in particular, system output of an implantable middle ear hearing device (IMEHD) by measuring a physical quantity that is relevant to the insertion gain and output level of the IMEHD when implanted in the patient. 1.2 This practice is similar to headphone calibration on an artificial ear in which the sound pressure level (in decibel sound pressure level (SPL)) measured in the artificial ear can be converted to patient hearing level (in decibel hearing level (HL)) using a known transfer function, as defined by ANSI 3.7. These measurements can then be used to predict system parameters relevant for patient benefit such as functional gain, maximum output, and variability. Measurements defined in this practice should be useful for patients, clinicians, manufacturers, investigators, and regulatory agencies in making comparative evaluations of IMEHDs. 1.3 The values given in SI units are to be considered the standard.