Section 16-B. Computation of pensions in certain retirement funds

Notwithstanding the provisions of any other law, general or special, the
  members of every teachers' retirement system in all cities of the  state
  shall, when retired pursuant to the law governing such system, receive a
  pension,  if  lawfully  entitled  thereto,  based  on the average annual
  compensation earnable as a teacher during  the  five  years  immediately
  preceding the date of his retirement, or the average annual compensation
  earnable as a teacher during any ten consecutive years of state service,
  said ten years to be selected by the member prior to date of retirement.