N.Y. Real Property Tax Law § 1803-A
(b) The current base proportion shall be determined pursuant to the following formula:
2. For the purposes of this section, the base percentage and the current percentage of each class and for each portion shall be computed pursuant to this subdivision.
(a) Base percentage. The base percentage for each class for each assessing unit and portion thereof shall be determined as follows:
(b) Current percentage. The current percentage for each class for each assessing unit and portion thereof shall be determined as follows:
3. Where there was no taxable real property in a class in a portion on the final assessment roll completed and filed in nineteen hundred eighty-nine, the local base proportion, base percentages and current percentages for such portion shall be determined as provided by this subdivision for each tax levy based upon an assessment roll filed subsequent to the assessment roll on which such property first appears.
(b) The base percentage for each class shall be determined as follows: