Rudi, you throw away everything you've already learnt about filing a chain, it'll only hinder you.
It's usually best if someone shows you first, you attack the chain in a totally different way to round filing and you have to so aware that you don't end up with a top or side beak.
I swear they look heaps better in real life than in photo's too
(But I reckon a photo is a damned good way to see if it does look ok, and I use a binocular magnifier when filing it)
I couldn't wait and had a go at it before Neil could show me, but I didn't get it finished in time for that particular training day so ran an aggressive round filed chain instead.