Ill. Admin. Code tit. 83 § 600.10
"An Act concerning public utilities" (Ill. Rev. Stat. 1981, ch. ch. 1112/3, pars. 1 et seq.) contains the following provisions:
"Service" is used in its broadest and most inclusive sense, and includes not only the use or accommodation afforded consumers or patrons, but also any product or commodity furnished by any public utility and the plant, equipment, apparatus, appliances, property and facilities employed by, or in connection with, any public utility in performing any service or in furnishing any product or commodity and devoted to the purposes in which such public utility is engaged and to the use and accommodation of the public.
The Commission shall have power to ascertain, determine and fix for each kind of public utility suitable and convenient standard commercial units of service, product or commodity, which units shall be lawful units for the purposes of this Act; to ascertain, determine and fix adequate and serviceable standards for the measurements of quantity, quality, pressure, initial voltage or other condition pertaining to the performing of its service or to the furnishing of its product or commodity by any public utility, and to prescribe reasonable regulations for examining, measuring and testing such service, product, or commodity, and to establish reasonable rules, regulations, specifications and standards to secure the accuracy of all meters and appliances for examining, measuring, or testing such service, product or commodity.
Ill. Admin. Code tit. 83, § 600.10