A tariff may provide rates from or to designated points by the addition or deduction of arbitraries or differentials to or from rates in the tariff form or to named base points. Provision for this shall be shown either in a separate item in the same tariff, which shall specifically name the base point and state the manner in which the arbitraries or differentials shall be applied, or in a separate rate basis tariff.
Ill. Admin. Code tit. 92, § 1225.505