Techniques · Easy
Hidden single
A hidden single is a digit that fits in only one cell of a row, column, or box. The cell may still look busy, because other digits haven't been ruled out of it yet. They don't matter. The digit has nowhere else in that house, so it is placed and the other candidates leave.
In a box, this is the move Quick puzzles are built from: find the digit that has one home in the box. A row or a column can hide a digit the same way, and that is what separates Easy from Quick.
When it shows up
Quick puzzles are solved with hidden singles inside boxes only. Easy puzzles also allow a hidden single in a row or column. Both stay inside singles, with no pointing and no pairs.
NYT Easy is singles only. Three of the 495 Easy puzzles place a line hidden single if lines are scanned before boxes, and those three still solve with box hidden singles alone.
See it on a real puzzle
The marks are the candidates left when this is the next step in the solve. Step through it: the pattern, what leaves, and what that forces.
See the pattern
Look at the 7s in this box.