Around 24 to 27 givens. Singles stop before the end; this is where writing notes starts to pay, because a pair is only visible in the notes.
New at this level
- Naked Pair — Two cells hold the same two candidates → erase that pair from the rest of the unit
- Hidden Pair — Two digits fit in only the same two cells → erase every other candidate from those cells
All levels
- Easy · naked singles only
- Medium · up to hidden singles
- Hard · up to pairs
- Very hard · up to intersections and triples
- Expert · up to advanced techniques
- How sudoku difficulty is graded