If you put a formula into a sheet  in a workbook linking to another workbook it
will ask you if you want to update  the links every time you open  it.

To create  this formula have both sheets open. Click the cell where you want
the result to be. Press = and then click the cell in the other workbook you
want to obtain the data  from. Then press enter.

Any reason why you've asked the same question on the same group, twice, but
with different subjects?