A representative example of binary evolution calculations. Left panel: the solid and dash-dotted curves show the mass-transfer rate and the mass of the helium layer on the WD varying with time after the helium star fills its Roche lobe, respectively. Right panel: the evolutionary track of the donor star is shown as a solid curve and the evolution of orbital period is shown as a dash-dotted curve. Dotted vertical lines in both panels indicate the position where the double detonation may happen. The initial binary parameters and the parameters at the moment of the SN explosion are given in these two panels.