Period Events

What variable type do you need to use in periodic events?
I can't seem to use the 'variable' option in selecting the time period for periodic events, as it says there are no defined variables of that type...
I've tried real and integer, and now I'm stumped...
So, what type should it be?

It should be a real value for periodic events, though you can't always use variables in GUI for everything.

It's a real, but for some reason, GUI doesn't like you using variables there. You'll have to use JASS to do so.

Edit: Heh, beat me to it.

Bugger. =P

I should really stop putting off learning JASS...

Anyway, thanks.