Evolution of the three axes R_i of an ellipsoid according to the homogeneously collapsing ellipsoid model (HCE; solid curve), and the five approximations considered in the text: Zeldovich (ZA; dotted curve), modified Zeldovich (MZA; short‐dotted curve), deformation tensor (DTA; dot‐dashed curve), complete Zeldovich (CZA; short‐dashed curve), and local tidal (LTA; long‐dashed curve). The initial axis ratios are 1:1.25:1.5, and the density contrast linearly extrapolated to ﹩a=1﹩ is ﹩\delta _{0}=1﹩. The ZA overestimates the collapse time, whereas all other approximations are close to the HCE.