The commission may, upon its own motion, at any time, and upon reasonable notice to any utility, when the commission deems it necessary to ascertain the value of the property of such utility, proceed to investigate, ascertain and report the value thereof, and shall make such investigation, ascertainment and report upon the request and application of any utility. To enable the commission to make such investigation and report, if upon its own motion, it may employ such experts and other assistants as it may deem necessary. If such investigation and report is made upon the application of a utility, the same shall be made and the experts and assistants employed by the commission for that purpose shall be employed at the expense of the utility making such application. The commission may appoint examiners who shall have the power to administer oaths, examine witnesses and take testimony in connection with any such investigation. In arriving at a valuation of the property of any utility as provided in this section, the commission shall give due consideration to the history and development of the utility and its property, original cost, cost of reproduction as a going concern and other elements of value recognized by the laws of the land for rate-making purposes. For the purpose of making such investigation, the members of the commission and its duly authorized agents and employees shall at all reasonable times have free access to the property, accounts, records and memoranda of the utility whose property and rights are being valued, and such utility shall aid and cooperate with the commission and its duly authorized agents and employees to the fullest degree for the purpose of facilitating such investigation. Upon the completion of the valuation of any utility, as provided in this article, the commission shall thereafter keep itself informed of all extensions and improvements or other changes in the condition and values of the property of such utility, and shall ascertain the value thereof, and shall from time to time revise and correct its valuation to the extent that may be necessary by reason of such extension and improvements or other changes in the physical condition and resulting value of such property; and to this end every utility shall make such report and furnish such information as the commission may require.