Strategy

•  Write each candidate in every unsolved square. Then look at the unsolved squares one by one, and see if you can eliminate any of the candidates by using the rule that no digit may appear more than once in any row or column, and every digit must appear exactly once in every row or column. When you have done this for every unsolved square, hopefully you will have been able to solve at least one of the squares. This new discovery should lead to even more using the same process as described above.

•  If any 2 squares in the same line have exactly 2 different candidates between them, then neither of those 2 candidates can be in any other square in the same line.
*Note: This rule applies for any number of squares.

Example: The far left box cannot be 2 or 4 because those numbers must be shared between the middle 2 boxes. Since 3 is already used, the far left box must be 1.

Special Candidates

Any Grid Size
In a 2x cage with 2 squares the candidates must be 1,2

In a 3+ cage the candidates must be 1,2

In a 3x cage with 2 squares the candidates must be 1,3

An L-shaped cage of 3 squares with a total of 3x must have the numbers arranged like this:

In a 4+ cage with 2 squares the candidates must be 1,3

An L-shaped cage of 3 squares with a total of 4+ or 2x must have the digits arranged like this:

In a 5x cage or a 5 cage the candidates must be 1,5

An L-shaped cage of 3 squares with a total of 5x must have the numbers arranged like this:

In a 6+ cage with 3 squares in a line the candidates must be 1,2,3
In a 6x cage with 3 squares in a line the candidates must be 1,2,3
In a 7+ cage with 3 squares in a line the candidates must be 1,2,4
In a 10x cage with 2 squares the candidates must be 2,5
In a 10x cage with 3 squares in a line the candidates must be 1,2,5
In a 15x cage with 2 squares the candidates must be 3,5
In a 15x cage with 3 squares in a line the candidates must be 1,3,5
In a 20x cage with 2 squares the candidates must be 4,5
In a 20x cage with 3 squares in a line the candidates must be 1,4,5

4x4 or Larger
In a 6+ cage with 3 squares in a line the candidates must be 1,2,3
In a 6x cage with 3 squares in a line the candidates must be 1,2,3
In an 8x cage with 3 squares in a line the candidates must be 1,2,4

3x3
An L-shaped cage of 3 squares with a total of 4x must have the numbers arranged like this:

4x4
In a cage of 2 squares with a total of 3- the candidates must be 1,4
In a 6+ cage with 2 squares the candidates must be 2,4
In a 7+ cage with 2 squares the candidates must be 3,4
In a 4x cage or a 4 cage with 2 squares the candidates must be 1,4
In a 6x cage with 2 squares the candidates must be 2,3
In an 8x cage with 2 squares the candidates must be 2,4

5x5
In a cage of 2 squares with a total of 4- the candidates must be 1,5
In a 6x cage with 2 squares the candidates must be 2,3
In a 9+ cage with 2 squares the candidates must be 4,5
In an 8+ cage with 2 squares the candidates must be 3,5
In an 8x cage with 2 squares the candidates must be 2,4
In a 12x cage with 2 squares the candidates must be 3,4
In a 12x cage with 3 squares in a line the candidates must be 1,3,4
In a 60x cage with 3 squares in a line the candidates must be 3,4,5

6x6
In a cage of 2 squares with a total of 5- the candidates must be 1,6
In an 11+ cage of 2 squares the candidates must be 5,6
In a 10+ cage of 2 squares the candidates must be 4,6
In a 15+ cage with 3 squares in a line the candidates must be 4,5,6
In an 18x cage with 2 squares the candidates must be 3,6
In an 18x cage with 3 squares in a line the candidates must be 1,3,6
In a 14+ cage with 3 squares in a line the candidates must be 3,5,6
In a 120x cage with 3 squares in a line the candidates must be 4,5,6

. .