Along a line the digit sits in one box only → erase it from that box outside the line.
Technique 7 in the order the hint searches · difficulty Very hard · up to intersections and triples
Turn the arrow around. If every cell that could take a 6 along some row is crowded inside a single box, the 6 has to appear on that row, and so it ends up inside that box.
Sweep one line from end to end
Split a row's nine cells into its three boxes and look for a digit whose candidates survive in only one box's share. The stage is the same three cells as the pointing pair, but you're looking from the opposite direction, which makes it easy to miss.
How the hint says it
Along column 7, every place 6 could go lies inside the middle-right box. 6 has to appear somewhere in that column, so it comes off the remaining cells of that box.
The line claims one seat in that box in advance
It is settled that the 8 goes on that row, and every place for it lies inside that box. So the 8 lands in one of the three cells where box and row overlap, and the box's other six cells cannot have an 8.
Very hard, the same as the pointing pair. Once you get into the habit of checking both directions, the number of puzzles that stall on you drops noticeably.
Puzzles that need this technique
Four puzzles with a spot where nothing moves until you use Box/Line Reduction. Press a number to play it.
- Practice 1 ·
3-6050327 - Practice 2 ·
3-4921849 - Practice 3 ·
3-4357610 - Practice 4 ·
3-2664893