Use this guide as a working method, not a list of tricks. Read one section, apply it to a real activity, and keep the evidence that shows why each move works.
The short answer
Locked candidates occur when every possible location for one digit in a box lies on one row or column, or when every location in a line lies inside one box.
For pointing, remove the digit from the rest of that line outside the box. For claiming, remove it from other cells inside the box.
Before continuing, open Medium Sudoku and practise this first move: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box. The complete activity makes the setup advice above easier to judge than an isolated example.
Track one digit and one box-line intersection at a time. Complete candidate maps are essential before eliminating.
Understand the exact job of this activity
In Locked Candidates in Sudoku: Pointing and Claiming Explained, success means you can recognize both pointing and claiming locked-candidate patterns, prove which candidate eliminations are valid and use the resulting reductions to reveal singles, pairs or other easier deductions without guessing. The relevant evidence is the digits already present in the same row, column and box, together with the candidates those digits eliminate. Decoration, familiarity with the theme and confidence are not evidence by themselves.
Use one cell together with its row, column and 3×3 box to keep the decision local. Start by doing this: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box. If you cannot name what changed, do not add another permanent answer or mark.
Measure progress by this standard: count justified placements and cleaned candidate sets rather than elapsed time alone. When progress stops, return to this method: apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line. State the reason for changing approach before you make the next move.
Prepare the materials and the decision record
For Locked Candidates in Sudoku: Pointing and Claiming Explained, lay out a partly solved Sudoku with current candidate notes, one digit selected for scanning, visible three-by-three box boundaries and an erasable or reversible way to remove candidates as each box-line relationship is verified. Keep any answer material closed or out of reach until the attempt has a complete result or a precisely stated question.
On paper, write candidates in consistent miniature positions and erase obsolete notes before they become clutter. On screen, select a cell, use notes for candidates and recheck highlighted peers after a placement. Check the real input method before starting so a print, zoom or touch problem is not mistaken for puzzle difficulty.
Record uncertain work this way: place a large digit only when the three units rule out every alternative; keep candidates small. If beginner-to-intermediate Sudoku solvers who already understand candidate notes and want a reliable bridge from singles into harder elimination techniques pause and return later, the record should show what is confirmed, what is provisional and what was rejected.
- Goal: recognize both pointing and claiming locked-candidate patterns, prove which candidate eliminations are valid and use the resulting reductions to reveal singles, pairs or other easier deductions without guessing.
- First action: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box.
- Working unit: one cell together with its row, column and 3×3 box.
- Final check: scan every row, column and box for duplicates, then compare the finished grid with the recorded solution.
Apply a pointing pair or triple
Step 1 - In one box, mark every legal position for digit 6.
Step 2 - Confirm that all marked positions lie on the same row.
Use Hard Sudoku for the next pass. Try to apply pointing logic by keeping the candidate in the aligned cells inside the box and removing that candidate from other unsolved cells farther along the same row or column outside the box, because the box must place the digit in one of its aligned positions without opening the answer material, then return here and name the evidence that supported the decision.
Step 3 - State that row must place 6 somewhere inside this box.
Step 4 - Remove candidate 6 from other cells in that row outside the box.
Step 5 - Recheck changed cells for singles and verify no box location was missed.
Worked example: 6 locked in the top-middle box
Suppose the top-middle box allows 6 only at r2c4 and r2c6. Both positions share row 2.
Remove candidate 6 from r2c1, r2c2 and any other row-2 cells outside that box.
Leave r2c4 and r2c6 unresolved. A later crossing decides which one contains 6.
Decision log for the worked example
For the Locked Candidates in Sudoku: Pointing and Claiming Explained example, log the first observation created by this action: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box. Write the observation itself, not a vague note that the step was completed.
Next, record what changed after you apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line. If nothing changed, keep that result; an explicit no-change result prevents the same unproductive pass from being repeated.
Close the log with the final check: scan every row, column and box for duplicates, then compare the finished grid with the recorded solution. If the check fails, identify the earliest unsupported decision and connect it to one risk: calling a candidate locked when the digit still has a possible position elsewhere in the same box off the shared row or column.
Diagnostic questions for Locked Candidates in Sudoku: Pointing and Claiming Explained
Can you explain why scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box is the correct opening for locked candidates sudoku? If not, restate the goal - recognize both pointing and claiming locked-candidate patterns, prove which candidate eliminations are valid and use the resulting reductions to reveal singles, pairs or other easier deductions without guessing - before making another mark.
Does the current record follow this rule: place a large digit only when the three units rule out every alternative; keep candidates small? If not, separate confirmed work from possibilities before the next method.
Which evidence supports the current decision: the digits already present in the same row, column and box, together with the candidates those digits eliminate? Remove any answer supported only by familiarity or appearance.
Have you checked for this specific failure: confusing pointing with claiming and eliminating from the wrong region of the grid? Repair that issue locally instead of restarting unrelated work.
Can the final result pass this test: scan every row, column and box for duplicates, then compare the finished grid with the recorded solution? If not, leave the activity marked as unfinished and record the exact failing unit.
Adjust difficulty without changing the core skill
For an easier sudoku activity, reduce clue count, candidate density, the solving techniques required and how many logical steps must be chained together while preserving the goal to recognize both pointing and claiming locked-candidate patterns, prove which candidate eliminations are valid and use the resulting reductions to reveal singles, pairs or other easier deductions without guessing. Keep the same opening method: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box.
For a harder locked candidates sudoku task, add one source of complexity at a time. Continue to require this evidence: the digits already present in the same row, column and box, together with the candidates those digits eliminate. More decoration, smaller print or longer instructions do not create useful difficulty.
Now compare the method on Easy Sudoku. Keep the goal—recognize both pointing and claiming locked-candidate patterns, prove which candidate eliminations are valid and use the resulting reductions to reveal singles, pairs or other easier deductions without guessing—but change only the difficulty or theme, so the comparison shows whether the routine transfers.
For beginner-to-intermediate Sudoku solvers who already understand candidate notes and want a reliable bridge from singles into harder elimination techniques, adjust the amount of material, available time or input method before removing the reasoning step. Assistance should make the evidence reachable without supplying the result.
Common mistakes and precise recovery actions
Watch for this first failure in Locked Candidates in Sudoku: Pointing and Claiming Explained: calling a candidate locked when the digit still has a possible position elsewhere in the same box off the shared row or column. Stop, restore one cell together with its row, column and 3×3 box and repeat this action: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box.
A second risk is confusing pointing with claiming and eliminating from the wrong region of the grid. Compare the current work with the digits already present in the same row, column and box, together with the candidates those digits eliminate; keep only decisions that the evidence supports.
If you notice removing the candidate from the aligned cells that establish the lock instead of preserving those candidate positions, return to this method: apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line. Record the corrected result before touching any later answer.
When using stale or incomplete pencil marks, which can make a false box-line restriction appear valid occurs, use this recovery procedure: remove the last unsupported digit, restore candidates in its row, column and box, and resume from the most recent proven placement. Continue only when the progress measure changes for a stated reason.
Prevent the final failure - finding a legitimate locked-candidate elimination and then continuing to hunt for advanced patterns without rescanning for the new single or pair it may have exposed - by completing this action: after each valid elimination immediately rescan the affected row, column and box for naked singles, hidden singles or newly exposed pairs, because the practical value of locked candidates is usually the easier deduction they create next. Then run the verification for locked candidates sudoku: scan every row, column and box for duplicates, then compare the finished grid with the recorded solution.
Build a checklist for Locked Candidates in Sudoku: Pointing and Claiming Explained
Write the Locked Candidates in Sudoku: Pointing and Claiming Explained goal first: recognize both pointing and claiming locked-candidate patterns, prove which candidate eliminations are valid and use the resulting reductions to reveal singles, pairs or other easier deductions without guessing. Under it, copy this opening action: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box. Leave space for the result, not merely a tick box.
Add the second and third checks in order: apply pointing logic by keeping the candidate in the aligned cells inside the box and removing that candidate from other unsolved cells farther along the same row or column outside the box, because the box must place the digit in one of its aligned positions; then apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line. Beside both, print the record rule: place a large digit only when the three units rule out every alternative; keep candidates small.
Reserve a separate line for the hard-area pass: verify the scope before every elimination: pointing starts from a box and eliminates along the line outside the box, while claiming starts from a row or column and eliminates elsewhere inside the box; never delete the candidate from the cells that prove the lock. Name the exact unit inspected so a later correction does not erase unrelated progress.
End the checklist with this action: after each valid elimination immediately rescan the affected row, column and box for naked singles, hidden singles or newly exposed pairs, because the practical value of locked candidates is usually the easier deduction they create next. Follow it immediately with the verification statement: scan every row, column and box for duplicates, then compare the finished grid with the recorded solution.
Test the checklist against the worked case - if candidate 4 appears only in two cells of the top-left box and both cells are on row three, 4 is locked to row three inside that box; remove candidate 4 from other unsolved cells on row three outside the box, then check whether any affected cell or unit has been reduced to a single legal option. Rewrite any item that still needs the full article to explain what object to inspect or when to stop.
- Open with: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box.
- Develop with: apply pointing logic by keeping the candidate in the aligned cells inside the box and removing that candidate from other unsolved cells farther along the same row or column outside the box, because the box must place the digit in one of its aligned positions.
- Discriminate with: apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line.
- Resolve with: verify the scope before every elimination: pointing starts from a box and eliminates along the line outside the box, while claiming starts from a row or column and eliminates elsewhere inside the box; never delete the candidate from the cells that prove the lock.
- Close with: after each valid elimination immediately rescan the affected row, column and box for naked singles, hidden singles or newly exposed pairs, because the practical value of locked candidates is usually the easier deduction they create next.
Teaching, family and group use
When demonstrating Locked Candidates in Sudoku: Pointing and Claiming Explained, model one complete unit: one cell together with its row, column and 3×3 box. Say which evidence matters, perform this action - scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box - and stop after the result is recorded.
For shared use, organise participation this way: one solver proposes a digit while the other names the row, column or box that proves it. Rotate responsibility after a small milestone so one person does not make and approve every decision.
If the step in “Teaching, family and group use” is still unclear, continue with How to Play Sudoku: A Beginner’s Guide. It approaches the same puzzle format from a different decision point before you need to reveal an answer.
If beginner-to-intermediate Sudoku solvers who already understand candidate notes and want a reliable bridge from singles into harder elimination techniques need help, ask what has been ruled out and which method comes next. Point back to apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line rather than revealing the solution.
At the end, ask which action changed the most information. Record one adjustment for the next sudoku page and keep private performance notes off public leaderboards.
A focused 15-minute practice routine
Minutes 0-3 for Locked Candidates in Sudoku: Pointing and Claiming Explained: prepare a partly solved Sudoku with current candidate notes, one digit selected for scanning, visible three-by-three box boundaries and an erasable or reversible way to remove candidates as each box-line relationship is verified. State the goal to recognize both pointing and claiming locked-candidate patterns, prove which candidate eliminations are valid and use the resulting reductions to reveal singles, pairs or other easier deductions without guessing, then identify the first one cell together with its row, column and 3×3 box you will inspect.
Minutes 3-7 for locked candidates sudoku: complete scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box, followed by apply pointing logic by keeping the candidate in the aligned cells inside the box and removing that candidate from other unsolved cells farther along the same row or column outside the box, because the box must place the digit in one of its aligned positions. Record both outcomes using this rule: place a large digit only when the three units rule out every alternative; keep candidates small.
Minutes 7-12: complete this action on the least certain result: apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line. If the evidence supports a next move, continue with verify the scope before every elimination: pointing starts from a box and eliminates along the line outside the box, while claiming starts from a row or column and eliminates elsewhere inside the box; never delete the candidate from the cells that prove the lock; otherwise keep the uncertainty visible.
Minutes 12-15: complete after each valid elimination immediately rescan the affected row, column and box for naked singles, hidden singles or newly exposed pairs, because the practical value of locked candidates is usually the easier deduction they create next. End the sudoku practice by checking that scan every row, column and box for duplicates, then compare the finished grid with the recorded solution, even when the full page remains unfinished.
Print, screen and accessibility choices
To print Locked Candidates in Sudoku: Pointing and Claiming Explained, follow this format rule: write candidates in consistent miniature positions and erase obsolete notes before they become clutter. Test one page at actual size and inspect the working area before producing a batch.
To use locked candidates sudoku online, follow this screen rule: select a cell, use notes for candidates and recheck highlighted peers after a placement. Verify keyboard, touch and mouse behaviour at the zoom level the player needs.
Accessibility support for beginner-to-intermediate Sudoku solvers who already understand candidate notes and want a reliable bridge from singles into harder elimination techniques should preserve the evidence - the digits already present in the same row, column and box, together with the candidates those digits eliminate - while changing size, contrast, input method or session length. Support access without silently supplying the answer.
Verify the confinement statement
A valid proof says where every source candidate lies and why the digit must remain within that box-line intersection.
Recompute the selected digit after elimination. One missed source location invalidates the lock.
Practise identifying pointing and claiming examples separately before scanning a hard grid for both.
Test the skill on a fresh puzzle
Open one linked sudoku page and write down two actions before starting: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box, followed by apply pointing logic by keeping the candidate in the aligned cells inside the box and removing that candidate from other unsolved cells farther along the same row or column outside the box, because the box must place the digit in one of its aligned positions. Put Locked Candidates in Sudoku: Pointing and Claiming Explained aside during the attempt.
At the first uncertain point, use this method without prompting: apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line. Compare one confirmed result with one unresolved result and name the evidence separating them.
Complete the fresh attempt by doing this: after each valid elimination immediately rescan the affected row, column and box for naked singles, hidden singles or newly exposed pairs, because the practical value of locked candidates is usually the easier deduction they create next. Run the same final check - scan every row, column and box for duplicates, then compare the finished grid with the recorded solution - and record one specific adjustment for the next page.
Frequently asked questions
What should I do first in Locked Candidates in Sudoku: Pointing and Claiming Explained?
Begin with the catalogued opening action for locked candidates sudoku: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box. Apply it to one cell together with its row, column and 3×3 box and record the result before moving to apply pointing logic by keeping the candidate in the aligned cells inside the box and removing that candidate from other unsolved cells farther along the same row or column outside the box, because the box must place the digit in one of its aligned positions.
How can I tell whether my locked candidates sudoku method is producing real progress?
For this sudoku task, use the progress test 'count justified placements and cleaned candidate sets rather than elapsed time alone'. A new mark counts only when it can be connected to the digits already present in the same row, column and box, together with the candidates those digits eliminate.
What should I do if I notice calling a candidate locked when the digit still has a possible position elsewhere in the same box off the shared row or column?
Stop at the first affected unit and use the format-specific recovery: remove the last unsupported digit, restore candidates in its row, column and box, and resume from the most recent proven placement. Resume Locked Candidates in Sudoku: Pointing and Claiming Explained with apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line instead of repeating the unsupported move.
When is it appropriate to check the answer for Locked Candidates in Sudoku: Pointing and Claiming Explained?
Check after completing this final action: after each valid elimination immediately rescan the affected row, column and box for naked singles, hidden singles or newly exposed pairs, because the practical value of locked candidates is usually the easier deduction they create next. Before opening the answer, write the exact unresolved point and test whether scan every row, column and box for duplicates, then compare the finished grid with the recorded solution.
How can I make this sudoku practice more accessible?
Change size, spacing, session length or input method while preserving the digits already present in the same row, column and box, together with the candidates those digits eliminate. On paper, write candidates in consistent miniature positions and erase obsolete notes before they become clutter. On screen, select a cell, use notes for candidates and recheck highlighted peers after a placement.
What should I practise after Locked Candidates in Sudoku: Pointing and Claiming Explained?
Choose a nearby locked candidates sudoku page and repeat two actions without reopening the article: scan one three-by-three box at a time for a candidate digit that remains possible only in cells lying on the same row or the same column; when every possible location for that digit in the box shares one line, the digit is locked to that line inside the box; then apply claiming logic in the reverse direction by scanning a row or column where all remaining positions for one candidate fall inside the same box; the digit must be placed somewhere in that box-line intersection, so remove the candidate from the other cells of that box outside the line. Finish by checking that scan every row, column and box for duplicates, then compare the finished grid with the recorded solution.
