The remainder of our discussion will focus on various methods available for calibrating the output during OAE measurements. Again, the discussion is presented so that the clinician is aware of the principles underlying various calibration techniques and is able to ascertain the impact of these different techniques on the recorded OAEs. Let us begin by restating the purpose of calibrating the output of an OAE system—to deliver an accurate stimulus signal to the patient’s tympanic membrane. Here the term accurate essentially covers three signal domains: (1) amplitude or level, (2) frequency, and (3) time. The temporal domain becomes most relevant in the case of OAEs recorded with brief stimuli, such as TEOAE. The domains of signal level and frequency are relevant to all stimuli used to record OAEs. Our discussion will focus on the complexities in delivering accurate stimulus levels across patients and across multiple measurements on the same patient. This focus is warranted because stimulus level is most variable across individuals and between tests. Intersubject variability is reflective of individual differences in ear canal geometry and volume, whereas intrasubject variability arises from differences in probe insertion and fit between tests.