Pencil marks: keep only useful candidates
Pencil marks are temporary possibilities, not permanent clutter. Add them when a cell has several plausible values, then remove them as soon as a peer placement rules one out.
Key idea
Treat note cleanup as part of every move: place, prune the row, prune the column, prune the box, then scan for singles.
See the move, step by step
Use the same real puzzle position to see how one placement changes notes across the grid.
Step 1 of 3
Notice every peer containing 5
R5C5 is a confirmed 5. Before placing it, notice the highlighted 5 notes in cells that share its row, column, or box; all of those notes are about to become impossible.
Step 2 of 3
Place the value, then prune its peers
Place 5 at R5C5. The highlighted 5 notes are now stale because every one of those cells sees the new 5; remove them before looking for the next move.
Step 3 of 3
Read the new singles
After candidate 5 is removed, R5C2 is left with 2, R6C4 with 9, and R7C5 with 3. Clean notes turn one certain move into three obvious next moves.
Try it on today's puzzle
Use notes only when direct scans stop producing placements. After every move, clear that digit from all peers before you continue.
Play today