In this technique you must find double with "mates" in a combination of Row Column Block.
The example below is a combination of a column and row.
3-6 have a mate in the row(7) that will lead to 7 if itself is 6. It also have a mate in Column(7) that will lead to a 7 if itself is 3.
One of the mates will be a 7 Therefore 7 can be eliminated in Row(1) Column(9)