From
the original 18 extremely difficult grids, I have engineered another 30+
grids. The game selector on the far left allows the user to load any of
the 50 stored grids.

All the other controls are for
re-engineering grids.

- Swap Block Rows/Column: A block consists of 3 rows or columns, i.e. block row 1 has rows A-C, block row 2 has rows D-F, block row 3 has rows G-I, block column 1 has columns 1-3, etc. A block swap will move 3 rows/column to another position.
- Shift: Each digit can be shifted by 1-9 then adjusted if greater than 9 by starting with 1 for 10, 2 for 11, 3 for 12, etc.
- 90/180/270: The entire grid can be rotated by intervals of 90 degrees.
- Swap Rows/Columns: Within row/column blocks, rows/columns can be swapped: row 1 can be swapped with rows 2 or 3, 2 can be swapped with 1 or 3, etc. Column 1 can be swapped with columns 2 or 3, column 2 can bet swapped with 1 or 3, etc.

The integrity of the solution remains as long as the occupied
block-row, block-column, row & column count remain constant.