Stepping Stone Methods :
This is a procedure of determining the optimal if any for improving each of the non basic variables in terms of the objective function. To determine this potential each of the non basic variables ( Empty cells ) is consider one by one. For each such well we find out as to what effect on the total cost would be if one unit is assigned to this cell. With this information then we come to know whether the solution is optimal or not. If not we improve that solution. To understand it we refer to the table a side which is a reproduction of the table above containing the initial basic solution obtained by NW corner rule.
In the above table there are four empty cells BD, CD, AF, BF,
The rule for testing the optimality is if none of the empty cell has a positive opportunity cost the solution is optimal. And if one ( or more ) of the empty cell have a positive opportunity cost the solution is not optimal and calls for revision. We concentrate only on the cells that have positive opportunity cost and would select the one with the highest value.