Section 19B. The board of library commissioners, in setting up minimum standards of free public library service and in certifying such libraries for aid under section nineteen A shall require the filing of an annual report and shall require that such public libraries
(1) be open to all residents of the commonwealth,
(2) make no charge for normal library services,
(3) be kept open a minimum number of hours per week,
(4) employ trained personnel in accordance with regulations promulgated by the board of library commissioners; provided, however, that in cities of more than one hundred and fifty thousand residents, nothing in said regulations shall prevent the appointing authority from employing a chief executive officer of the library system in addition to the chief librarian,
(5) expend a reasonable portion of the library’s total budget on library materials,
(6) lend books to other libraries in the commonwealth and extend privileges to the holders of cards issued by other public libraries in the commonwealth on a reciprocal basis,
(7) include in their annual report the total number of nonresident loans and nonresident circulation as a percentage of the library’s total circulation, as certified by the librarian and subject to an audit by the state auditor.