Figure 3-10. Example of an earplug fitting and educational pack.
d. The accuracy of the audiometer must be checked at least once a week; this is
easily done by testing two young persons with no history of ear disease or hearing loss
and a known hearing threshold level (HTL). Such a procedure checks not only the
accuracy of the instrument, but also the effectiveness of sound insulation in the test
room. The results should be within 5 dB of HTL level of the individual at each test
frequency. Failure to obtain such results indicates either incorrect audiometer
calibration or excessive room noise, or both. The audiometer should be calibrated
periodically, at least semiannually for self-recording audiometers, and annually for
others by a qualified medical equipment repair facility.