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-� — arithmetically, and tlie results then expressed in decibels. The restriction on averaging pertains only to processing of the fundamental pressure squared variable. Statistical processing of sampled derived measurements, such as an ensemble of Leq.T values, is not similarly restricted. The forn�ula used for this task was as follows: Leq.T = 10 log [ 1T OT lOLp(t)/10 dt] = 10 log [Tl OT [ p(t)po]2dt] To further explain the above formula consider the defining furnction where Lp (t) is sound pressure levels as a function of time, '1' is the observation or averaging time, p(t) is sound pressure as a function of time and po is the reference pressure of twenty (20} micropascals ( Pa}. Adoption of the-equivalent sound level terminology was likeJy lnotivated to forestall erroneous use of the arithmetic averaging. Nevertheless, the term average sound level is also in wide use and is functionally identical. Tn an actual circumstance where sou��d levels could be variable, the equivalent sound level equals a constant sound level that appropriately inte�ated over the averaging time would result in the same energy as integrating the corresponding variable sound level over the same time. In contrast, for sound levels stated for discrete time increments, the overall equivalent level can be obtained by the fol(owing combining relationship. The levels for each discrete time period may be constants or may themselves be equivalent levels. Thus the combined equivalent level is (A-weighted levels used in the following example): N LAeq.T = 10 log [ 1T ti 10 LAi/l OJ I =1 The ultimate result of this type of testing is to oblain sound readings that can be used to establish exposure levels. This exposure level of sound dose can also be stated in joules. Regulatory agencies nonnalize the allowed ]imit by stating it as percentage dose, where a dose of 1Q0% corresponds to an exposure at the criterion level (Lc) for a duration equai to the criterion time (Tc), which is nonnally speci�ed as eight {8) hours. However, at stated earlier, in this case the tar�et dose will be the immediate, short term, 100% pealc level achieved at any given point during the sampliiig episode. Therefore, the noise level results are all stated in decibels. As such a decibel {dB) is a unit for measuring the intensity of sound. The decibel is a dimension less quantity, based on the logarithm of the ration of two power-like quantities. Considering the lluman hearing range is theo��etically from zero (0) dB (theoretical threshold of audibility) to one hundred and thiny (130) dB, the average pain threshold, a cornparison can be shown. Sound power (W) of a source is the tota] acoustic output that it produces in watts (w). For most practical situations the sound power of a souree is constant regardless of its location in difEerent environments. The amplitude of the sound pressure disturbance can be related to the displacement amplitude of the vibrating sound source. Pressure is expressed as force per unit area. The preferred unit of pressure is lcnown as the pascal {Pa) or one newton per square metzr (N/m2}.