Reconstructed intermediate period based on reconstructing the second phase of mass transfer (y-axis) versus expected intermediate period based on the assumption that the first phase of mass transfer was stable (x-axis). The diamond shapes indicate the possible values for the observed systems for different assumptions. Lowering the metallicity lowers both periods, while increasing M₂ lowers only the values on the y-axis. Top right of each diamond thus is for solar metallicity and M₂ = 1 M_⊙ and bottom left is for intermediate metallicity and M₂ = 2 M_⊙. The shading indicates that, very broadly, the upper parts are more likely scenarios (see text). If all systems were formed through stable mass transfer, all shapes should intersect with the diagonal. Systems 1, 16, and 17 have identical masses and thus fall on top of each other.