I've created my own Sudoku solution and grid to assist solving these puzzles and they include macros.
I the individual boxes I can have the numbers, 1, 2, 3, 4, 5, 6, 7, 8, 9 and when I have figured out a number in another cell, I remove it from the ones in the same 9 squares and from the Horizontal row and column.
However, I've somehow picked up a formatting issue not of my own doing and would like to know how it is doing what it is.
When I am removing a number from my list and press Enter, an information box headed Sudoku pops up with the message, you can only enter whole numbers from 1 to 9.
It wasn't me that created it, I can't find it in any macro, not conditional formatting