N.Y. Real Property Tax Law § 1905
2. Base percentage. The commissioner shall compute for each such approved assessing unit or eligible non-assessing unit village and for each portion thereof the percentage that the estimated taxable market value of each of the homestead class and non-homestead class constitute of the total estimated taxable market value of all real property. Such base percentage shall be computed on the basis of the assessed valuations on the first assessment roll containing the revaluation or update which is the basis for the certification or recertification of such assessing unit as an approved assessing unit, except that:
5. Computation of adjusted homestead base proportions and adjusted non-homestead base proportions. In each year in which it is required to compute a current percentage pursuant to subdivision one or three of this section, such commissioner shall compute the adjusted homestead base proportion and adjusted non-homestead base proportion as follows: