First question: The magnitude of current flowing in a circuit is described in units of Amperes. The device used to measure it is an Ampmeter, or Ammeter.
Second question: This question is so absurd that it should not be dignified with an answer. Although 'E' is often used as the symbol for Electromotive force, potential difference, and voltage, there's certainly no rule. Anyone is free to use 'M', 'Q', 'Θ', or 'Щ' to denote voltage when they write electrical formulas, just as long as they make sure to explain the meaning of whatever symbols they use.
