This work examines two important factors in calculating paramagnetic chemical shifts from the computational methods. Firstly, the choice of formalism (VV, mPV and BB) used to model the magnetic properties of the paramagnetic center and the shifts is crucial. The three approaches listed here are not entirely equivalent and may give substantially different results depending on a particular system. These difference has recently given a lot of discussions about which is the "correct" formalism . These discussions are focused primarily on dipolar based shifts in metalloproteins, here we expand the discussion to more general systems also with substantial Fermi-contact shifts. Secondly, even when the proper formalism is identified then the choice of computational methods has also a large influences on the calculated shifts. Specifically the choice of DFT functionals and basis sets have a substantial impact on the hyperfine tensors.