Parity

Par"i*ty (?), n. [L. paritas, fr. par, paris, equal: cf. F. parité. See Pair, Peer an equal.] The quality or condition of being equal or equivalent; A like state or degree; equality; close correspondence; analogy; as, parity of reasoning. "No parity of principle." De Quincey.

Equality of length and parity of numeration.