Mass. Gen. Laws ch. 54 § 25
The aldermen or selectmen shall cause each polling place in their respective cities and towns to be provided with a sufficient number of suitable marking shelves or compartments where voters may conveniently and secretly mark their ballots; and they shall cause a guard rail to be so placed that only persons inside thereof can approach within six feet of the ballot boxes or of the marking shelves or compartments, or of the voting machines if any are used. The ballot boxes, marking shelves or compartments and voting machines, if any are used, shall be in view of persons in the polling place outside the guard rail. The number of marking shelves or compartments shall be not less than one for every seventy-five voters at such polling place, and not less than five in any voting precinct of a city, and not less than three in any town or voting precinct thereof, except that, where voting machines are used, only one such marking shelf or compartment need be provided, which shall be for the use of challenged voters. Every marking shelf or compartment shall at all times be provided with proper supplies and conveniences for marking the ballots. Where voting machines are used, one voting machine shall be provided at each polling place for every four hundred voters, or the major part thereof, entitled to vote therein.
Where electronic voting systems are used, if the system requires the use of a special marking unit, such units shall be supplied to a number of not less than one for every one hundred and twenty-five voters.
Mass. Gen. Laws ch. 54, § 25