Section 121. The person designated to make such examination and test may at any reasonable time enter upon the premises where the meter to be inspected is placed for the purpose of making the inspection. He shall receive such compensation for his services as the department may determine, together with his necessary traveling and other expenses, which shall be audited by the department and paid by the commonwealth; but the total amount of compensation and expenses shall not exceed three thousand dollars in any year; and if the total amount of such compensation and expenses shall in any year exceed the amount of the fees received for such examinations and tests, the excess shall be assessed and recovered from the electric companies in the manner now provided for the assessment and recovery of the other expenses of the department. The department may establish such rules and regulations, fix such standards, prescribe such fees, and employ such means and methods in, and in connection with, such examinations and tests of electric meters as it deems most practicable, expedient and economical. The department may purchase such materials, apparatus and standard measuring instruments for such examinations and tests as it deems necessary.