How to change the index for git status?

Hi,

When I run git status, it show the status compared against the branch
upstream/develop. I want it to compare against origin/develop. I
checked progit. But I don't see how to change the branch to compare
to. Could anybody let me know how to do so? Thanks!

~/dvcs_src/craftyjs1/Crafty/build/api$ git status
# On branch 2D_doc_dev
# Your branch is ahead of 'upstream/develop' by 2 commits.
#
nothing to commit (working directory clean)


-- 
Regards,
Peng