Jon M,
I suspect that is for a loco number 4. It is the loco entry in the roster.
Opening the file with a text editor should show the top of the file. If the
first couple of lines show something about 'locomotive' then it is a loco.
But if the first couple of lines talk about 'roster', then it is a roster
index. You don't want to move that, use the 'Rebuild roster index' to make
sure it matches the contents of the roster directory.
-Ken Cameron, Member JMRI Dev Team
www.jmri.org
www.fingerlakeslivesteamers.org
www.cnymod.com
www.syracusemodelrr.org
Ken Cameron