Rate of change of the orbital period (upper panel) and orbital speed aΩ (bottom panel) compared to the rate of stellar mass change. In the gray shaded region, the mass of the donor star changes faster than the orbital period or speed. The two limit cases are the conservative mass transfer (dotted line, RLOF) and the pure mass loss without accretion by the secondary (solid blue line). In between, the green and red solid lines correspond to an accretion efficiency by the secondary of 5% and 50%, respectively. The arrows indicate that as mass transfer proceeds, the mass ratio can only decrease.