You can do it in one instance of excel:
Open both workbooks, resize EXCEL (the app, not the file) and widen it so it
spans both monitors, then use Window/Arrange/Tiled and each will be on a
separate monitor. Now you CAN copy/paste formulas!
I do it all the time!
Bob Umlas
Excel MVP

"Helen" wrote in message
...
When I need to work in two separate Excel files on two separate monitors,
here's something I do:

StartRunExcel. Take that instance of Excel and drag it to one monitor
(downsize it first).
Again, click StartRunExcel; this will open a new instance of Excel.

Open your Excel files. You can now work in two separate files.

Remember: when working with dual monitors, you cannot copy/paste a
formula
from one file to another.