This document defines and compares various units and scales used to measure noise levels and loudness perception, including: - Phon and Sone, which measure loudness level (LL) and sone, respectively. Sone is defined as the loudness of a 1 kHz tone at 40 dB. - LAeq, the equivalent continuous A-weighted sound level, which represents the steady dB(A) level that would produce the same sound energy over a given time period as a time-varying sound. - LPN, the perceived noise level scale, which measures the perceived noisiness of aircraft by observers on the ground using loudness summation and conversion to Noy units. - L