The first pass is a main slice.
The next pass is the lowest step-cutting slice.
and
The next passes are the step-cutting slices up to the previous main slice.
The next main slice.
The main slices are cut from top to bottom as normal. The intermediate slices are cut from bottom to top. This is possible because the depth of cut is always less than the depth of cut (or Stepdown) for the main slice. This is the most efficient way of cutting the part as it reduces the number of passes and increases the depth of cut of each pass.