Sudoku technique guide

Single Digit Chain Sudoku Technique

A Single Digit Chain follows one candidate through strong and weak links. This guide explains the idea in plain English, when to look for it, and the common mistake to avoid.

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At a glance

Difficulty

Advanced

This is where Single Digit Chain normally sits in a human solving path.

Family

Visual chain techniques

It belongs to the visual chain techniques group of Sudoku logic.

Main action

Usually remove candidates

Most technique moves reduce notes first. That often reveals a simpler placement afterwards.

What is Single Digit Chain?

A Single Digit Chain follows one candidate through strong and weak links.

The important thing is that this is logic, not guessing. You are using the current candidates to prove that a number must either go in one place, or cannot stay in another place.

In SudoSketch, this technique is designed to work with notes and Coach highlighting, so the key cells and removal cells can be shown clearly.

How Single Digit Chain works

Focus on one candidate only.
Follow strong and weak links through the grid.
Use the chain endpoints to prove a candidate can be removed or sometimes placed.

When to look for it

Look for Single Digit Chain after easier moves have stopped working. First check for naked singles, hidden singles, locked candidates and simple pairs. If those do not move the puzzle forward, this technique may be worth checking.

For learning, do not try to scan for every advanced technique at once. Pick one method, understand the shape, and practise spotting that one pattern.

Common mistake

Do not mix candidates. The chain follows one digit only.

If you are unsure, rebuild the candidates first. Bad notes create bad logic, and Sudoku will absolutely punish you for it like a tiny spreadsheet goblin.

Single Digit Chain FAQ

What is Single Digit Chain in Sudoku?