Section 56. Every fifth year, the commissioner shall certify as to whether the board of assessors is assessing property at full and fair cash valuation. Once certified, a city or town may classify in the manner set out in this section for the year of certification and for the 4 years following said year of certification. The selectmen or town council of each town and the city council together with the mayor's approval in each city, which city or town has been certified by the commissioner of revenue to be assessing property at full and fair cash valuation, shall annually first determine the percentages of the local tax levy to be borne by each class of real property, as defined in section two A of chapter fifty-nine, and personal property for the next fiscal year; provided, however, that if the mayor vetoes the city council's percentages, in a city, the city council may override such veto with a vote equal to two-thirds of the members elected. In determining such percentages, the selectmen, town council or the city council, together with the mayor's approval, as the case may be, shall first adopt a residential factor; provided, however, that if the mayor vetoes the city council's factor, in a city, the city council may override such veto with a vote equal to two-thirds of the members elected. Said factor shall be an amount not less than the minimum residential factor determined by the commissioner of revenue in accordance with the provisions of section one A of chapter fifty-eight and shall be used by the board of assessors to determine the percentages of the local tax levy to be borne by each class of real and personal property. Prior to the adoption of such percentages, the selectmen, town council or the city council, as the case may be, shall conduct a public hearing on the question of their adoption. At such hearing, the board of assessors shall provide all information and data relevant to making such determination and the fiscal effect of the available alternatives. The commissioner of revenue shall not approve the tax rate of a city or town under section twenty-three of chapter fifty-nine until the selectmen, town council or the city council, as the case may be, have held such a public hearing and until the city or town has adopted the percentages of the local tax levy to be borne by each class of real and personal property.

Class one percentage, the full and fair cash valuation of the class one property divided by the full and fair cash valuation of all real and personal property in said city or town multiplied by the residential factor.

Class two percentage, the full and fair cash valuation of the class two property divided by the full and fair cash valuation of all real and personal property in said city or town multiplied by not less than seventy-five per cent of the residential factor.

Class three percentage, the full and fair cash valuation of the class three property divided by the sum of full and fair cash valuation of class three and class four real property and personal property in such city or town multiplied by the difference between one hundred per cent and the sum of the class one and two percentages.

Class four percentage, the full and fair cash valuation of the class four property divided by the sum of the full and fair cash valuation of the class three and class four real property and personal property in such city or town multiplied by the difference between one hundred per cent and the sum of the class one and class two percentages.

Personal property percentage, the full and fair cash valuation of the personal property in a city or town divided by the sum of the full and fair cash valuation of the class three and class four real property and the personal property in a city or town multiplied by the difference between one hundred per cent and the sum of the class one and class two percentages.

As used in this section the full and fair cash valuation amounts shall be those amounts as determined by the commissioner of revenue and sent to each city and town pursuant to section one A of chapter fifty-eight.

The percentages, so determined, shall upon certification of the commissioner be transmitted to the board of assessors to be used in setting the tax rates pursuant to section twenty-three A of chapter fifty-nine.

Notwithstanding the first paragraph, the commissioner may, from time to time, issue a revised schedule for the year in which the commissioner shall certify whether the board of assessors is assessing property at full and fair cash valuation. After the schedule is issued, a city or town may classify in the manner set forth in this section for any year before the next year of certification established in the schedule for the city or town. In arranging the schedule, the commissioner shall, so far as is practicable and appropriate, consider at least the following goals: balancing the number of certification reviews conducted in each year of the 5–year period; facilitating and implementing joint or cooperative assessing agreements or districts; assisting the boards of assessors to comply with minimum standards of assessment performance established under section 1 of chapter 58; and producing uniformity in the valuation, classification and assessment of property within each city or town and throughout the commonwealth.