Left: the current mass normalized by the mass at first crossing, M _now/M _FC, as a function of time since first crossing (t _FC). The color represents the three-dimensional acceleration (km s⁻¹ Gyr⁻¹) at the first crossing moment. M _now/M _FC is well correlated with the acceleration at first crossing. We further divide our sample according to t _FC and the mass ratio M _now/M _FC as shown by the boxes numbered from one to five for further analyses; the divisions are made at t _FC = 3 and 6 Gyr and M _now/M _FC = 1. Right: the histogram of the mass ratio M _now/M _FC. For most halos, their current mass has not evolved much compared to the mass at first crossing.