HTC Tilt 2 User Manual page 259

Appendix 59
Hearing devices may also be rated. Your hearing device manufacturer or hearing
health professional may help you find this rating. Higher ratings mean that the
hearing device is relatively immune to interference noise. The hearing aid and
wireless phone rating values are then added together. A sum of 5 is considered
acceptable for normal use. A sum of 6 is considered for better use. A sum of 8 is
considered for best use.
In the above example, if a hearing aid meets the M level rating and the wireless
phone meets the M level rating, the sum of the two values equal M5. This should
provide the hearing aid user with "normal usage" while using their hearing aid with
the particular wireless phone. "Normal usage" in this context is defined as a signal
quality that is acceptable for normal operation.
The M mark is intended to be synonymous with the U mark. The T mark is intended
to be synonymous with the UT mark. The M and T marks are recommended by the
Alliance for Telecommunications Industries Solutions (ATIS). The U and UT marks
are referenced in Section 0.19 of the FCC Rules. The HAC rating and measurement
procedure are described in the American National Standards Institute (ANSI) C6.19
standard.
For information about hearing aids and digital wireless phones
FCC Hearing Aid Compatibility and Volume Control:
http://www.fcc.gov/cgb/dro/hearing.html
Gallaudet University, RERC:
http://tap.gallaudet.edu/DigWireless.KS/DigWireless.htm