Sudoku-YFoundations
Scanning Sudoku: follow one digit to find a first move
If the whole board feels busy, follow one digit first. You do not have to inspect every empty cell at once.
Use the clues that already exist
Rows, columns and boxes cannot repeat digits. A placed digit therefore rules out that same digit along its units. Start with a box missing the digit you are following. Choosing a frequently placed digit can provide useful restrictions, but does not guarantee a move.
Our partial example
The top-left box is missing 7. Its empty cells are A1, A2, B2, C1 and C3. Given A7=7 and C6=7, rows A and C cannot hold another 7. This removes all the listed positions except B2, so the box forces B2=7. We are finding a place for one digit, rather than guessing the contents of a cell.
When two places remain
Keep both candidates. Check crossing columns or move to another digit. After placing a value, revisit the affected units; you need not restart a complete board scan. This is our suggested workflow, not a rule requiring one fixed solving order.
Notes are not placed clues
A pencilled 7 at A7 does not forbid 7 elsewhere in row A. Also check that the source box has not already received its 7. Try the Singles exercises next to compare a cell with one candidate and a unit with one position for a digit.
Try before looking
Try before revealing
If C2 becomes another empty cell while C6 remains a placed 7, does the conclusion change?
Show explanation
No: row C still excludes C2. Adding B1 as another valid position for 7 would change it, since B2 would no longer be the only place.
References and further reading
Read the source explanations and compare them with our examples. Links are references, not endorsements or claims of affiliation.