Samsung SCH-S950RKATFN - Manual (Page 154)

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device with your hearing device is the best way to evaluate it for
your personal needs.
M-Ratings: Wireless mobile devices rated M3 or M4 meet FCC
requirements and are likely to generate less interference to
hearing devices than mobile devices that are not labeled. M4 is
the better/higher of the two ratings. M-ratings refer to enabling
acoustic coupling with hearing aids that do not operate in telecoil
mode.
T-Ratings: Mobile devices rated T3 or T4 meet FCC requirements
and are likely to generate less interference to hearing devices
than mobile devices that are not labeled. T4 is the better/higher
of the two ratings. T-ratings refer to enabling inductive coupling
with hearing aids operating in telecoil mode.
Hearing devices may also be rated. Your hearing aid
manufacturer or hearing health professional may help you find
this rating. Higher ratings mean that the hearing device is
relatively immune to interference noise.
Under the current industry standard, American National
Standards Institute (ANSI) C63.19, the hearing aid and wireless
mobile device rating values are added together to indicate how
usable they are together. For example, if a hearing aid meets the
M2 level rating and the wireless mobile device meets the M3
level rating, the sum of the two values equals M5.
Under the standard, this should provide the hearing aid user with
normal use while using the hearing aid with the particular
wireless mobile device. A sum of 6 or more would indicate
excellent performance.
However, these are not guarantees that all users will be satisfied.
T ratings work similarly.
The HAC rating and measurement procedure are described in the
American National Standards Institute (ANSI) C63.19 standard.
M3 + M2 = 5
T3 + T2 = 5