Mass. Gen. Laws ch. 211, § 24
(c) A retired chief justice or associate justice so serving shall be paid by the commonwealth, in addition to the pension or retirement allowance received, a per diem differential rate of compensation equivalent to one two hundred twentieths of the balance remaining after deducting the annual pension or retirement allowance received from the current annual salary of such justice if not retired. The per diem differential rate of compensation shall be paid monthly from Judiciary appropriated funds.
Such retired justice shall be entitled to all other benefits of a regular incumbent of the supreme judicial court and shall be reimbursed for expenses incurred while performing such services at any place other than his place of residence. While so serving he shall be entitled to receive such staff support, clerical assistance and facilities as are customarily available to judges of the court on which he serves.