How to jump with ediff

[Haines Brown]

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

However I do not know how to jump from one diff to the next. I read 
that it is done with the n and p keys, but I cannot do it because the 
file is writable. To act on differences a file must be writable.

What I would like to do is jump to the next diff in one window in sync 
with a jump to that position in in the other window so that I am 
automaticall looking at the same region in both so that I can can use 
what I see in own to edit th other. Are synced jumps possible?

Haines Brown