Hi all. I received my GX7 on Friday and have been trying to figure it out. There are some things that I'm having trouble getting used to, coming from an Olympus camera. One thing is the lack of ISO fine-tuning. On the Oly I regularly shoot at 640, 1000, 1250, 2000, etc. The GX7 seems to only go full stops, 400, 800, 1600 etc. But, I have seen several reviews, blog posts etc. that reference having shot at 640, so I am wondering: Is there some advanced menu to enable this?