point gride for help

[clin-fu]

The value of K theoretically can be approximated by the total number of points(P) divided by the number of cells in the grid (N3) (i.e.K ≈ P/N3 ). When working with point clouds of size P = 1024,we empirically set K = 4 with a grid size of 16 × 16 × 16 for the best trade-off between accuracy and performance
why?? 1024/161616=1/4????