20.0.2. For the purposes of taxation of the sale of movable property that is delivered on a continuous basis by means of a wire, pipeline or other conduit and for which an invoice is issued for a period commencing before 1 January 1991 and ending after 31 December 1990, the tax provided for in this chapter shall be computed as if an equal part of the whole of the property sold were sold on each day of the period.