GreatCall Jitterbug How-To Manual page 167

sum of 6 is considered for best use.
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.
156 Health and Safety Information