I am using a chevron for hiding and collapsing an area on my interface. I have found versions of chevrons out there that use 2, and others that use a single:
Is there any standard or reason to favor one over the other?
I highly recommend doing some A/B testing on simple things like these. That being said, they wont make a significant difference between users unless there is some ambiguity in the interface.
Typically I'd use the double-chevron when the distance of collapse is larger (
You might have noticed that there's a gap from 25–50%, where I use my gut instinct.