N.Y. Real Prop. Tax Law § 842
The commissioner shall compute county equalization rates for each county to which this title is applicable by furnishing the final state equalization rates which are established pursuant to article twelve of this chapter for each city and town in the county for the final assessment roll to be completed and filed during the current year or, if such rates are not then available for each city and town in the county, by adjusting the final state equalization rate established pursuant to article twelve of this chapter for each city and town in the county for the final assessment roll required to be completed and filed during the prior calendar year by the appropriate "change in level of assessment", if any, as that term is defined in section twelve hundred twenty of this chapter. On or before the fifteenth day of November, or such other date as may be prescribed by law for the determination of county equalization rates, the commissioner shall certify the county equalization rates to the clerk of the legislative body of each county to which this title is applicable. Within five days of the receipt of such rates, the clerk of the legislative body shall provide to each city and town a written notice of the county equalization rates computed by the commissioner.
N.Y. Real Prop. Tax. Law § 842