Section 10(2)(a) in Kolkata Municipal Corporation Act, 1980
(a)such number of persons, not being less than five and more than seven, as the Corporation may determine, to be elected by the members of the Corporation from amongst themselves in accordance with the system of proportional representation by means of the single transferable vote and the voting at such election shall be by secret ballot. The members of the Mayor-in-Council shall not be eligible for such election; and