At the 5th square the red coloured 3 is the only possible number that fits in that cell.

Number 1 and 4 are eliminated by the column. Number 5, 7 and 8 are eliminated by the row. Number 2, 6 and 9 are eliminated by the square. So the only option left is number 3.

At the 4th square the red coloured 7 is the only possible number that fits in that cell.

Because of the 7 at the 1st square the 7 at the 4th square can not be in the mid-column of the square. Because of the 7 at the 5th square the 7 at the 4th square can not be at the 1st row of the square. Because of the 7 at the 6th square the 7 at the 4th can not be at the last row of the square. So the only option left for number 7 is at the first cell of the mid-row.

At the 3rd cell of the 1st square the red coloured 6 can be removed from that cell. So the only option at the 3rd cell of the 1st square is number 9.

Due to the limitations at the 3rd square number 6 must appear at G1 or H1. So the possibility of number 6 at C1 can be removed. After this the only number that fits in cell C1 is number 9.

The red coloured numbers 1 and 4 will be removed from the possitiliy list due to the presence at G2 and H2.

Because G2 and H2 will contains the number 1 and 4. So the other cells, e.g. G1, H1 can not contain the number 1 and 4 any more. Due to this rule 1 and 4 can be removed from the possiblity list of those cells.

The red coloured numbers 1, 5 and 7 will be removed from the possitiliy list . The end result is 4 and 6 is possible for cell A and for cell C.

If you watch the possibilities of this row carefully. You will notice that 4 and 6 is only possible at cell A and cell C. Therefore number 5 is not possible for cell A. So do the numbers 1, 5 and 7 for cell C.

The red coloured numbers 1 and 4 at E and F can be removed from the possitiliy list . The end result is 2, 5 and 8 for cell E and 2, 5 and 8 for cell F.

If see watch the possibilities of this row carefully. You will notice that cell A , C and G forms a cycle of 3 different possibilities. Number 1, 4 and 6 belongs to A, C and G. The these numbers are not possible for cell E and F. Therefore you can remove these numbers from the possibility list of E and F.

This ultimate technique has been developed by our team. This technique will be used when level 1 to 6 techniques are not sufficient to solve the sudoku puzzle.