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c <br />-29- <br />in wide use and is generally accepted throughout the acoustical <br />field. <br />Subpart 5, item B provides that automated or integrating <br />measuring devices may use the check -off method described in <br />FHWA-DP-45-lR, Section 3.6 or be operated in accordance with the <br />manufacturer's recommendations for determination of an hourly <br />Leq. It is reasonable to allow the check -off method to be used <br />with automated measuring devices because those devices may be <br />operated on either a manual or automatic mode. When measuring <br />devices are used in the automatic mode (in this mode both data <br />and time are determined automatically) the measuring device is <br />independent; therefore, it is necessary and reasonable to follow <br />the manufacturer's recommendations. <br />Subpart 5, item C allows equivalent methods to be used but <br />provides that. the Agency Director must determine whether the <br />method is equivalent. It is necessary to allow the use of <br />additional monitoring methods to accommodate changes in sound <br />measuring devices. It is reasonable to have these additional <br />methods reviewed and approved by the Director to ensure that the <br />methods are equivalent to required methods and that they yield <br />representative data. <br />Subpart 6 provides for the calculation of Ldn. A formula is <br />provided in this subpart to clarify mathematical and time based <br />parameters necessary to calculate the Ldn. The Ldn formula set <br />