(a)
(1) Nothing in this act shall be taken to prohibit a public utility from establishing or entering into an agreement for a fixed period for a sliding scale or automatic adjustment of charges for public utility service in relation to the dividends to be paid to stockholders of the public utility, or the profit to be realized, or its expenses of operation to be incurred, or other equitable or reasonable basis for the scale or adjustment if a schedule showing the rates under the arrangement is first filed with and approved by the commission.
(2) Nothing in this section shall prevent the commission from revoking its approval at any time and fixing other rates and charges for the product or commodity or service if, after reasonable notice and hearing, the commission finds the existing rates or charges unjust, unreasonable, insufficient, or discriminatory.
(b) The commission shall have the power to fix a reasonable and just sliding scale of rates for public utilities.