How to jump with ediff

[Haines Brown <haines@histomat.net>]

I split a buffer horizontally and want to use ediff to find a
difference in a file displayed in one window and use that
information to edit a version of that file displayed in the other 
window. 

Simple enough but I do not know how to jump from one difference to the 
next. I read that this is done with the n and p keys, but I cannot do 
that because the files are writable. How does one jump from one 
diff to the next in ediff? Do I have to make the window in which I 
view a diff unwritable and the window in which I edit the file writable?

What I would ideally like to do is jump to the next diff in one window 
in sync with an automatic movement on the other window to the same 
position so that information on one file can be used to edit the 
other. Are synced jumps possible?

Haines Brown