An assembly of electronic reference devices intended to be used by a healthcare provider in a clinical setting to verify the performance of and/or calibrate and assess the electroacoustic frequency and sound intensity characteristics emanating from a hearing aid or group auditory trainer. The device typically consists of an acoustic complex of known cavity volume, a sound level meter, microphone, oscillators, frequency counters, microphone amplifiers, distortion analyser, chart recorder, and a hearing aid test box; some types may include a probe microphone used for real-ear measurement (REM). It does not measure hearing acuity [i.e., it is not an audiometer].