Figure 4.  The mass per nucleon parabola for the isobars at A = 27 after subtracting Coulomb energy, Ec.  For comparison, the values of M/A are shown for unbound nucleons on the left at Z/A = 0 for 1n = 1.008665 amu and on the right at Z/A =1 for 1H - Ec = 1.007071 amu.