Section 57G. The permanent, full-time fire chief or chief engineer of a fire department in any city, other than Boston, or town or fire district, and the permanent, full-time chief of police or superintendent of police, or city marshall, in any city, other than Boston, or town shall receive an annual base rate of compensation which shall not be less than the following ratios of the highest annual rate of compensation of a permanent, full-time firefighter, or a permanent, full-time police officer or patrolman, as the case may be:
1. In departments having less than twelve permanent, full-time police officers or firefighters, the ratio shall be: 1.5.
2. In departments having not less than twelve nor more than twenty-nine permanent, full-time police officers or firefighters, the ratio shall be: 1.8.
3. In departments having thirty or more permanent, full-time police officers or firefighters, the ratio shall be: 2.0.
The provisions of this section relative to a city, town or fire district shall be in effect only in a city, town or fire district which accepts this section.