Inside a box the digit sits on one line only → erase it from that line outside the box.
Technique 6 in the order the hint searches · difficulty Very hard · up to intersections and triples
Say a 4 could go in two or three cells of some box, and all of them lie on the same row. The 4 has to appear somewhere in that box, so it ends up on that row one way or another.
Take one box and check where each digit can sit
Split a box's nine cells into its three lines and look for a digit whose candidates all crowd into one of them. The three cells where box and line overlap are this technique's stage. You only have to study one box, so it gets fast with practice.
How the hint says it
In the top-center box, every place 8 could go lies on row 1. 8 has to appear somewhere inside that box, so it comes off the remaining cells of that row outside the box.
The box claims one seat on that line in advance
It is settled that the 3 goes inside the box. Since every place for it lies on column 2, the 3 lands in one of those three cells of column 2, so the other six cells of column 2 cannot have a 3.
Needing this much makes a puzzle Very hard. It's the first technique that looks at a box and a line together, and your field of view widens a step.
Puzzles that need this technique
Four puzzles with a spot where nothing moves until you use Pointing Pair. Press a number to play it.
- Practice 1 ·
3-9435761 - Practice 2 ·
3-8871522 - Practice 3 ·
3-8307283 - Practice 4 ·
3-7743044