Tier 2 · first asked for by Moderate
Pointing Pair/Triple
If every home for a digit inside a box lies on one line, the digit leaves the rest of that line.
Also called Pointing Pair, Pointing Triple, Locked Candidates Type 1.
Look at one digit inside one box. If the only cells that can take it all sit in the same row — or the same column — then wherever it eventually goes, it goes on that line. It is therefore not anywhere else along the line, outside the box.
Nothing gets placed here. The whole value is in the candidates you rub out, which is often what unlocks a single somewhere else entirely. This is the first technique that needs pencil marks to be worth anything.
A worked example
A real position, with the pencil marks a solver would have at that point.
the pattern · what it rules out · 5 a candidate that goes
What it proves. In box 3, 3 can only sit in R2C9, R3C9, all on column 9, so 3 leaves the rest of that column.