Mass. Gen. Laws ch. 218 § 52
In addition to the powers conferred in section ten of chapter two hundred and eleven B, the chief justice referred to in section fifty-one A may from time to time make assignments for the attendance of a justice at the several times and places appointed for holding court. Said chief justice, or, in case of his death, illness, absence or incapacity, the senior justice in the department, if in his opinion the public business so requires, may provide for additional sessions in the department. A special justice appointed in the district court department, with the assent of the chief justice for that department, may hold any such additional session at the request of the chief justice or senior justice as aforesaid. During the continuance of such request a special justice shall have and exercise all the powers and duties of a justice. The fact of holding court and the fact which gave him jurisdiction shall be entered upon the general records of the court, but need not be stated in the record of any case heard by him. The compensation of said justice shall be at the rate by the day of the salary of an associate justice of the municipal court of the city of Boston; and, except when holding an additional session as above provided, the compensation for service in excess of the number of days of vacation leave he has accumulated which may be rendered to or for any one justice shall be deducted from the salary of such justice; provided, however, that if such justice is absent due to his illness or physical disability for a period not exceeding the number of days of sick leave he has accumulated, no such deduction shall be made.
Mass. Gen. Laws ch. 218, § 52