There shall be a board of assessors which shall consist of three (3) members elected for terms of three years each, so arranged that one term shall expire each year. The board of assessors shall annually make a fair cash valuation of all property, both real and personal, within the town, and it shall have all of the powers and duties which are given to boards of assessors under the constitution and laws of the Commonwealth of Massachusetts, and such additional powers and duties as may be authorized by the charter, by by-law or by other vote of the town meeting.