The case notes
Every small square needs all three bands
Every overlapping two-by-two square contains a low digit (1–3), a middle digit (4–6), and a high digit (7–9). Watch a worked example, then try the idea in a puzzle.
Put it into practice
Every 2×2: low + middle + high
Global entropy applies to every two-by-two square in the grid, including overlapping ones. Each needs a low, middle and high digit.
High + low → middle needed
Here, seven and nine are high. One is low. The fourth cell has to be middle: four, five or six.
5 and 6 used → 4
The row already holds five and six. So this middle digit is four.
Overlapping square needs low
Shift the two-by-two square one cell to the right. Nine is high; four and six are middle. This time we need a low digit.
1 and 2 used → 3
One and two are already elsewhere in the top row, leaving three. Every overlapping square gets checked in turn.
Read the transcript
Global entropy applies to every two-by-two square in the grid, including overlapping ones. Each needs a low, middle and high digit. Here, seven and nine are high. One is low. The fourth cell has to be middle: four, five or six. The row already holds five and six. So this middle digit is four. Shift the two-by-two square one cell to the right. Nine is high; four and six are middle. This time we need a low digit. One and two are already elsewhere in the top row, leaving three. Every overlapping square gets checked in turn.
