Samsung SWC-R640LBAXAR - Manual (Page 219)

Health and Safety Information 214
A sum of 5 is considered acceptable for normal use. A sum of 6 is
considered for best use.
In the above 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 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 mobile device.
“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.
M3 + M2 = 5 T3 + T2 = 5