User's Manual

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.