Mass. Gen. Laws ch. 32 § 45C
In any city or town which has accepted sections forty-four and forty-five A in the manner set forth in section forty-five and which accepts this section in the manner hereinafter provided, the pension payable to a person retired under said section forty-four shall be one half of the highest annual compensation received by him while holding the grade held by him at the time of his retirement if he has completed twenty years of service, and an additional amount equal to one per cent of said annual compensation for each year of service after the first twenty; provided, that the total amount of such pension shall in no case exceed sixty-five per cent of said annual compensation.
This section shall take effect in a city having a plan D or plan E charter by the affirmative vote of two thirds of all the members of the city council, and in the case of any other city by vote of the city council, subject to the provisions of its charter, and in a town by a majority vote at an annual town meeting.
Mass. Gen. Laws ch. 32, § 45C