@JBeaucaire:
just a guess on my part though. you could be right. IF i am guessing right again, your new formula doesn't help too because it is now catered only to 1 region. selecting all region or multiple regions now won't work.

@FlameRetired:
i see that your profile states MS-Off Ver 2007 & 2013. PowerPivot is available in the 2013 by default using my steps. in 2010, you have to download it as a free add-in. in 2007, it is not available. you could try this method too:
https://support.office.com/en-us/art...8-fc4798f39ea8