Problem using file lists with imarith

[TonyRodda]

Hi, I'm a complete newbie trying to apply a (spectroscopic) master zero file to a number of files (.fit) which generates a new set of files. I can't seem to get the sytax right so any help would be greatly appreciated.
I've started by creating the input file list as >> files abcde*.fit > @list_mylist
This generates a text list which is expected.
I've used >> imarith @list_mylist - masterbias.fit @list_newlist doesn't work, Pyraf just skips to a new line.
I've used >> imarith list_mylist.list - masterbias newlist.list doesn't work either"
Varying combinations produce "Wrong number of elements in the operand lists".
Any pointers would be appreciated.
regards
Tony