Explicit relations between the spectroscopic constants, A͂ , B͂ , C͂, ⊿J,⊿JK, ⊿K, δJ,and δK, obtained by the application of the various reduction procedures of the effective rotational Hamiltonian are given in matrix formulation. Watson’s reduction procedures for the three different axis representations Ir, IIr, and IIIr have been considered as well as the reduction making R͂5 = 0, instead of R͂6 = 0. The ambiguity in the determination of the τ’s arising from the use of planarity conditions is discussed in relation to the τ defect.