Could anyone explain how this thing works?

http://www.peppervirals.com/viralgallery/Html.htm

Here's a clue, look at the symbol that is next to 9. The symbol in the magic square will always be that symbol, the one next to number 9. Note which other numbers have the same symbol next to them as does the number 9.

Wow! I didn't realize that they change. (I am having a blonde week ). Thank you for that.

but what if you picked a number which will give another symbol?

you cant the second number will bring it to a number with a zero at the end and the first number will bring it to a selected number with the simbol all the possible numbers that it could be have the same simbol.

Old trick.
There only 13 (14?) possible answers, all of them are the same symbol.
Every time you reload the page, the symbol changes.