
Pointing 

If the only instances of a candidate within a box are in the same row or column, you can eliminate candidates of that value from any other cell in the respective row or column. Consider the above example. In the bottomright box the only two 9's, highlighted in blue, are in the same column (column H). Thus the candidate 9 can be eliminated from H3 because it is also in that column. This is because regardless of which blue cell is 9, the green 9 gets eliminated.
Because the only result of this technique is the elimination of a candidate, it requires either all the candidates to be filled in or the direct result of a hidden single to be spotted. Sudoku Snake gives it a skill value of 9.






