6. "Base assessment roll" means:

1. (a) in the case of an assessing unit initially certified as an approved assessing unit on the basis of a revaluation or an update, the assessment roll completed in the year immediately preceding the first year of the revaluation or update which is the basis for certification as an approved assessing unit;
2. (b) in the case of a recertified approved assessing unit, the assessment roll completed in the year immediately preceding the update which is the basis for the most recent recertification as an approved assessing unit or the assessment roll specified in paragraph (a) of this subdivision; and
3. (c) in the case of an eligible non-assessing unit village, the village assessment roll or part of the town assessment roll used to levy the village tax in the year immediately preceding the first year.

13.

1. (a) "Homestead class" means (1) all one, two or three family dwelling residential real property, including such dwellings used in part for nonresidential purposes but which are used primarily for residential purposes, and farm dwellings; (2) all other residential real property consisting of more than three dwelling units held in condominium form of ownership, provided that, in other than approved assessing units which have adopted the provisions of section nineteen hundred three of this article prior to April thirtieth, nineteen hundred eighty-three, no such dwelling unit previously was on an assessment roll as a dwelling unit in other than condominium form of ownership, and provided further that the governing body of an approved assessing unit which, prior to April thirtieth, nineteen hundred eighty-three, has adopted the provisions of section nineteen hundred three of this article may by local law adopted after a public hearing prior to the taxable status date of such assessing unit next occurring after December thirty-first, nineteen hundred eighty-three, provided that all such property on the assessment roll of such assessing unit on April thirtieth, nineteen hundred eighty-three shall not be classified in the homestead class; (3) all vacant land parcels located in an assessing unit which has a zoning law or ordinance in effect, provided that such parcel is located in a zone that does not allow a residential use other than that described in subparagraph one of this paragraph, provided further, that such parcel does not exceed ten acres; and (4) land used in agricultural production which is eligible for an agricultural assessment pursuant to section three hundred five or three hundred six of the agriculture and markets law, where the owner of such land has filed an annual application for an agricultural assessment, and farm buildings and structures thereon, as defined in subdivision three of section four hundred eighty-three of this chapter.
2. (b) Notwithstanding the provisions of paragraph (g) of subdivision twelve of section one hundred two of this chapter, a mobile home or trailer shall not constitute a homestead for purposes of this article unless it is owner-occupied and separately assessed.

15. "Initial percentage" means the taxable assessed value of the real property in a class in an approved assessing unit or portion thereof or in an eligible non-assessing unit village divided by the taxable assessed value of the real property in the approved assessing unit or portion thereof or in the eligible non-assessing unit village 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:

1. (a) in the case of eligible non-assessing unit villages, such initial percentage shall be computed from the assessments on the village portion of the first town assessment roll containing revaluation assessments and used for the levy of village taxes;
2. (b) in the case of recertified approved assessing units which adopt local laws pursuant to subparagraph (ii) of paragraph (a) of subdivision two of section nineteen hundred three of this article, such initial percentage shall be computed from the assessed valuations on the first assessment roll containing the update which is the basis for recertification as an approved assessing unit; and
3. (c) where a base percentage was established pursuant to subdivision two of section nineteen hundred five of this article, as such subdivision existed on March thirty-first, nineteen hundred eighty-nine, for the roll to which the initial percentage is applicable, the initial percentage shall mean such base percentage.