Hi, I found a little strange that the manual says to fill the whole display for custom white balance. It's quite hard to do it with a small gray card without dropping shadows over it. So I did a couple of test shots to see if I could use a smaller area as it happens with other cameras. And yes, it looks like only the central area of a 3x3 grid is used (approximately). I do not know if/how much this is well known.