Nev. Admin. Code § 445B.390
For the purposes of section 2, unless the Director allows for the use of a different time period upon determining that the period is more representative of the normal operation of a source, the average rate, in tons per year, at which an emission unit actually emits a criteria pollutant during the consecutive 24-month period immediately preceding a date and which is representative of the normal operation of a source shall be deemed the actual emissions of the emission unit on that date. For the purpose of this section and section 2 of this regulation, actual emissions must be measured using the actual emissions of the emission unit or calculated using the emission unit's actual operating hours, production rates and types of materials processed, stored or combusted during the selected time period, as appropriate.
Nev. Admin. Code § 445B.390
NRS 445B.210, 445B.300