{ } - What do these do if they are around a formula?
 

I have a spreadsheet that was made by someone else and it has a formula which
is inside { }. When I click on the cell and click out on another cell the
formula no longer works (the formula did not change) but it works if I hit
undo. What is the deal?

{ } - What do these do if they are around a formula?
 

The curly braces around a formula indicate that it is an array formula.
You do not type the braces yourself - instead, when you type in the
formula you finish (or commit) it by pressing CTRL+SHIFT+ENTER (CSE)
rather than just <enter. This automatically wraps { and } around the
formula if you do it correctly. If you click into the formula bar, as
if to edit the formula, the curly braces disappear and the formula does
not work, so you would have to do CSE again.

Hope this helps.

Pete