"Last remaining cell" Sudoku Technique

The “Last Remaining Cell” Sudoku strategy is one of the first techniques beginners should learn. It is based on rules that no numbers should be duplicated in any 3×3 box, vertical column, or horizontal row. With a clear understanding of this rule, it allows players to eliminate and identify the correct cell location for each number.

If you now look at the below example, you will notice that there is a missing a 7 in the highlighted column, but there are 7’s elsewhere on the board. By remembering that numbers 1-9 cannot be duplicated in any box, column or row, and by looking at the placement of the 7’s outside of the highlighted column, we can identify the only suitable cell within the highlight column to place the 7.