4. Section 4 of the Principal Act is amended by inserting in subsection (1) the following definition:“ ‘average unimproved value', in relation to a parcel of land for a particular year, means—
(a) where the parcel has not been rateable previously—the unimproved value of the parcel;
(b) where the parcel has been rateable for less than 3 years—the average unimproved value of the parcel over those years; or
(c) in any other case—the average unimproved value of the parcel over the 3 years immediately preceding the particular year;
disregarding any fraction of a dollar;”.