Proceedings involving the reasonableness of existing or proposed rates vary so greatly in character and scope that it is impossible to prescribe rules of universal application that are suited to all rate proceedings. These proceedings range all the way from a simple proposal to change a rule which would increase or decrease the bills being paid by a few consumers to a broad proceeding involving all of the rates of a utility rendering service in the entire State. The former may require only one brief hearing because of the simplicity of the questions involved. The latter, as the experience of the commission has demonstrated, may consume years, require scores of hearings and thousands of pages of testimony preceded by long and tedious investigations of property, inventories and values together with extended analyses of operating costs, etc. Because of these facts, no attempt is here made to specify the data that must be supplied in all rate proceedings, but the following are of general application. Possibly the only one of universal application is the one first mentioned [see section 61.1 of this Part] which finds its origin in the Public Service Law.