Ps.
You may want to drop the checkbox and just use a cell that's formatted nicely.
(Saved from a previous post.)
You may find it easier to use a cell and a Y or X or any character to indicate
yes. You'll be able to sort, filter, and even count these easier than using
checkboxes.
An alternative that I like:
Select the range that would have held the checkboxes.
Format|cells|number tab|custom category
In the "type:" box, put this:
alt-0252;alt-0252;alt-0252;alt-0252
But hit and hold the alt key while you're typing the 0252 from the numeric
keypad.
It should look something like this when you're done.
ü;ü;ü;ü
(umlaut over the lower case u separated by semicolons)
And format that range of cells as Wingdings (make it as large as you want)
Now, no matter what you type (spacebar, x, anyoldtextatall), you'll see a check
mark.
Hit the delete key on the keyboard to clear the cell.
If you have to use that "checkmark" in later formulas:
=if(a1="","no checkmark","Yes checkmark")
Or you can filter by blanks and non-blanks.