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Let's Make Number Place (Elementary course)
Strategy Guide
Number Place Strategy Guide
Localization
When the placement of a number is limited to a specific location that prevents the number from appearing in squares aligned with that location.
Say a number can only appear in one three-square horizontal or vertical line of a 3 x 3 square. You can determine that the number will not appear again in the same line and can therefore ignore it as a candidate for squares in the same line.
Example 1
Pay attention to the number 3 in the upper left. Due to its influence, the number 3 can only be entered into the blue squares of the upper center 3 x 3 block.
Since one of the blue squares must be a 3, the rest of the squares in the same vertical line as the blue squares cannot be 3. You can safely remove 3 from the candidate numbers of the magenta squares.
Example 2
Pay attention to the circled 3 and the vertical line on the extreme left. The number 3 must go into one of the blue squares. Therefore, you can safely remove 3 from the candidates for the other squares in the block.