This Recommendation describes the preferred method for calculating loudness ratings mainly in the case of local telephone systems which transmit a band of frequencies not exceeding about 180 4500 Hz. The purpose of using loudness ratings for telephone sets is two-fold: first, to provide the transmission planner with an adequate measure of how the sets perform in the network; second, to enable valid and unambiguous comparison between sets. Therefore, to avoid confusion, this version of this Recommendation contains only those telephone set loudness ratings which are of interest for these purposes. The current revision of Recommendation P.79 is intended to clarify the application fields for Annexes A and G. The Recommendation incorporates in Annex A the description of narrow-band Loudness Ratings which is applicable for narrow-band and "dual-Mode" narrow-band / wide-band end to end transmission, including terminals. Annex G is intended to apply only for end to end wide-band transmission ( 100Hz to 7 kHz ) between wideband terminals.