First we constructed a parent simulation of sufficient size to include thousands of Milky Way sized systems but also of sufficient resolution to construct good Lagrangian volumes. We decided on ~10,000 particles per Milky Way-sized host and a 100 Mpc/h volume. Our level_max=10 , which means our parent simulation’s effective resolution is (2^10)^3 = 1024^3, i.e. a parent particle mass,