  The origin and calibration of the maximum absolute magnitude relation with
decline time (MMRD) for novae, first derived by Zwicky (1936) empirically
validated by McLaughlin (1940) and widely used to estimate distances to
classical novae and the near-constancy of the absolute magnitude of novae, 15
days after optical maximum, suggested by Buscombe and de Vaucouleurs (1955) are
revisited in this paper and found to be valid. The main results presented in
the paper are: (1) A physical derivation of the MMRD based on instantaneous
injection of energy to the nova system. (2) A significantly better-constrained
MMRD: M_{V,0} = 2.16(+-0.16)log_{10}t_2 - 10.804(+-0.117) using a two step
calibration procedure. (3) It is shown that the MMRD is one of the best
distance estimators to novae available to us and that accuracy of the distances
is predominantly limited by an underestimated peak apparent brightness. (4) It
is shown that the same MMRD calibration is applicable to novae of all speed
class and to both Galactic and extragalactic novae. (5) It is shown that the
absolute magnitudes of novae with 2.4 < t_2 < 86$days have a smaller scatter on
day 12 (M_{V,12} = -6.616 +-0.043) compared to day 15 following optical
maximum.
  We reiterate the need for homogenised high fidelity spectrophotometric data
in optical bands on classical and recurrent novae in outburst to effectively
utilise the potential of the MMRD and M_{V,12} in determining their
luminosities and distances.
