Let's see - how to explain this...
Your helper lists all the possible numbers that could go in a square, but sometimes in a bigger square of 9 individual squares, a particular number might appear as a possible in only one out of the nine squares.
When this happens it obviously means that that number must go in that square, so the other "possibles" for that square are in fact impossibles, and probably shouldn't be listed.

Anyway, it's pretty good for free!! I'll be sending the link to my father - you should see his crappy method of figuring them out..

And it lets you put in zero as a number, and letters of the alphabet, and multiple-digit numbers, and even words and sentences and your own name (this IS fun! - I thought sudoku was boring!).

Rather useful tool saves the boring part of finding possible numbers for each square and the mess of writing them in by hand.

A suggestion. Rather than leaving blanks in the squares where numbers are already defined it would be useful to show the defined number in a large font that fills the square. Would save having to write them in after printing the result.

tru even nos are easier to get than odd try it and see