I have a long formula (below) that I want to be able to
use on any worksheet (current, previously saved, or new).
How can I save it or store it so that it is always
available, like the pull down lists in Functions. I know
this is probably a very basic operation, but I'm not up on
too much beyond the basics of EXCEL.

=MID(LEFT(CELL("filename",A1), FIND ("]", CELL
("filename",A1))- 1), FIND("[",CELL("filename", A1))+1,
255)

Thanks,
Joe B