- Rows 1–3 form the "top band" — three rows sharing three boxes
- Each box in the top band interacts with 6 rows and 9 columns outside it
- Completing any one row or box in the band immediately constrains the other two
- The same logical approach works for every band and every stack in the grid
- You do not need to start at the top — but filling a full band creates useful cascades
What Is the Top Band?
The top band consists of rows 1, 2, and 3. These three rows intersect with the top-left box (R1–3, C1–3), the top-center box (R1–3, C4–6), and the top-right box (R1–3, C7–9). Every digit placed in any of those three boxes affects all three rows simultaneously.
Scanning the Top Band
For each digit 1–9, check which of the top-band boxes already contain it. Suppose digit 7 appears in the top-left box. That means 7 cannot go anywhere else in rows 1, 2, or 3 within that box — but more importantly, it also restricts where 7 can go in the top-center and top-right boxes.
If digit 7 also appears in a column that passes through the top-center box, you can eliminate that column's cells in the top-center box too. If only one cell in the top-center box remains, place 7 there.
Using Completed Rows to Force Placements
If row 1 has 8 given digits, row 1's last empty cell is forced immediately. That placement removes a candidate from its column and box — which may force another placement in row 2 or row 3. Work these forced moves in sequence rather than skipping to a different area of the grid.
Box Interactions in the Band
When a digit in one box of the top band is confined to a single row (e.g., digit 4 can only go in row 2 within the top-left box), that digit is eliminated from all cells in row 2 within the top-center and top-right boxes. This is the locked candidates pattern and it is one of the most useful in band analysis.
Why Band Logic Scales to the Full Grid
The same analysis you apply to the top band works for the middle band (rows 4–6), the bottom band (rows 7–9), the left stack (columns 1–3), the center stack (columns 4–6), and the right stack (columns 7–9). Once you understand band logic, you understand roughly half of all intermediate Sudoku techniques.
Practice this in a live puzzle at Medium difficulty, where band interactions appear regularly. The techniques library covers locked candidates and other band-based patterns in detail.