Commerce order rule save order I have a field in my orders which should be updated when an order is saved. I created a rule with the event "commerce order save", do the calculation for the field and at least save the order. But that logically gives me an endless loop.

How can I save the order without firing the event again?
You can use the 'Before saving a commerce order' trigger in Rules.  It's right there in the 'Commerce Order' section.  Then you don't need a save action since it's about to be saved already...

That should do it for you!