The tariff charged for the electricity by the New Zealand Electricity Department to the supply authority that supplies the electricity; and

A further sum or tariff sufficient to meet the actual cost incurred by that supply authority in delivering the electricity to the corporation:

Provided that, where on the 21st day of October 1966 (being the date of the commencement of the Electricity Amendment Act 1966) the price or tariff charged by a supply authority to a corporation was in excess of the said aggregate, the amount of the excess shall be reduced by equal annual amounts during the period of not more than five years commencing with the 1st day of April 1967 until no such excess exists.”