"The proper selection of base values is fundamental to the usefulness of a per-unit system. Although per-unit quantities have been used for many years by designers of rotating machinery, the base quantities were not standardized, and it was necessary to define them in each publication. A working group of the Rotating Machinery Committee was created to propose a set of standard definitions. In 1961, a proposed standard was published for trial use. A critical review of that proposed standard resulted in ANSI/IEEE Std 86-1975. Recently, systems analysts and some designers of rotating electrical machinery have found it useful to have a single generic model for all types of machines. Therefore, alternate per-unit definitions, using input voltamperes as base power for induction motors, have been included in this new revision, as well as an example of an induction generator."