User talk:Ruoxi Jia

- Quantities expressed as per-unit are the same when reflected from one side to another. - Similar apparatus will have impedances within a narrow range, but not necessarily the same. - Impedance and admittance are not independent.
 * Revise the introduction part, correct some misleading contents.
 * Add a paragraph of how to understand the essence of per unit system.
 * Extend the first purpose of per-unit system.
 * Emphasize that base values can only be magnitude.
 * Cite two rules in Power System Analysis and Design (By Glover, Sarma, Overbye) for base quantities
 * Correct the wrong format of the first reference
 * Cite Power System Analysis and Design, whose per-unit chapter is well-written.