=[test.xls]sheet1!A1

Is it possible to make the "sheet1" portion of this formula tied to a cell
in the destination workbook so that if I type "sheet2" in cell A3 of my
destination sheet, it will show what is in cell A1 of =[test.xls]sheet2!A1

What I am trying to do is make all the references in my workbook dependent
on what sheet# I have typed into cell A3. Up till now I have been fetching
all the data based on a 4 digit date format such as "0513". "0513" would be
the name of a sheet that was saved with data for may 13th. My hope is to be
able to type 0513 into cell A3 and have it reference the data. Can this be
done or is there a better way?

Also I noticed that in order to update the formula cell I have to select the
test workbook in the dialog box each time. Is there a way to make this a
constant reference instead of having to ok it? Hopefully without having to
open the reference workbook each time either?

I am rather new to this...

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Thank you!