This is a procedure of determining the potential 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 considered one by one. For each such cell well find out as to what effect on the total cost would be if one unit is assigned to this cell. Within this information then we come to known whether the solution is optimal or not. If not we improve that solution. To understand it we refer to the example containing the initial basic feasible solution obtained by least cost rule.