Public Utilities. Regulation: Rates. Reduction Order Affecting Rates Established by Commission in Prior Formal Proceedings Cannot Be Made Retroactive to Beginning of Current Proceedings; Charitable Contributions May Be Disallowed from Expenses; Investment Tax Credit Reduces Current Tax Expense. Pacific Tel. & Tel. Co. v. Public Util. Comm'n, 401 P. 2d 353, 44 Cal. Rptr. I (1965)