A systematic reevaluation of taxable real and personal property undertaken by the assessor, whether of specific areas in which real property is located or of specific classes of real or personal property to be assessed, shall be made only in accordance with a resolution or other act of the assembly directing a systematic reevaluation of all taxable property within the borough over the shortest period of time practicable, as determined by the assembly and fixed in the resolution or other act of the assembly. [Code 1974 §45.11.075.]