Samsung SCH-R631DWACRI - Manual (Page 112)

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In the above example, if a hearing aid meets the M2 level rating and
the wireless phone meets the M3 level rating, the sum of the two
values equal M5. This is synonymous for T ratings. 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 20.19 of the FCC Rules.
The HAC rating and measurement procedure are described in the
American National Standards Institute (ANSI) C63.19 standard.
Other Medical Devices
If you use any other personal medical devices, consult the
manufacturer of your device to determine if it is adequately shielded
from external RF energy. Your physician may be able to assist you in
obtaining this information. Switch your phone off in health care
facilities when any regulations posted in these areas instruct you to
do so. Hospitals or health care facilities may be using equipment that
could be sensitive to external RF energy.