In 1937, Rudolf E. Langer suggested a correction ℓ ℓ ( ℓ ℓ + 1 ) → → ( ℓ ℓ + 1 2 ) 2 which is known as Langer correction or Langer replacement. This manipulation is equivalent to inserting a 1/4 constant factor whenever ℓ ℓ ( ℓ ℓ + 1 ) appears. Heuristically, it is said that this factor arises because the range of the radial Schrödinger equation is restricted from 0 to infinity, as opposed to the entire real line. By such a changing of constant term in the effective potential, the results obtained by WKB approximation reproduces the exact spectrum for many potentials. That the Langer replacement is correct follows from the WKB calculation of the Coulomb eigenvalues with the replacement which reproduces the well known result.