Tier 1 · first asked for by Gentle
Hidden Single (line)
Within a row or column, a digit that can only go in one cell belongs there.
The same deduction as a hidden single in a box, along a row or a column instead. Take a digit missing from the line and check its nine cells; if only one can take it, that is where it goes.
These are harder to see than the box version, because a row spans the whole grid and the eye has further to travel. That is the only reason the two are graded apart.
A worked example
A real position, with the pencil marks a solver would have at that point.
the pattern · what it places
What it proves. 1 can only go in R8C7 within row 8.
Builds on Hidden Single (box).