Electrochemical cell potentials — an arbitrary zero and an intensive quantity

E⦵ values measure the tendency of a half-reaction to occur as a reduction, all referenced to an arbitrary zero (the standard hydrogen electrode). Hard because: the zero is a convention, not a physical fact; E⦵ is intensive so you must not scale it when balancing electrons (unlike ΔH); the sign of E⦵ flips when you reverse the half-equation but the magnitude does not; and it connects to ΔG through ΔG⦵ = −nFE⦵ with a minus sign that has to be right.