M(R) dependence for the exact solution of the TOV equations obtained using a unified EOS and for our approximate approach, for the DH and NL3ωρ models of dense matter. Solid black curves indicate the M(R) calculated with a unified EOS, solid blue curves indicate the M_core(R_core) relation, dashed red lines indicate the M(R) approximation based on Eqs. (11), (12), and the black lines indicate the exact solution of the TOV equation.