This is a formula I us daily

(example)
='V:\Production Reporting Summaries\Tammy\April 05\[Production
Summary.xls]4_04'!$B$4

each day I have to make a copy the previous days worksheet and then go into
multiply cells and change 4_04 to the next day, which would be 4_05.

I want to be able to enter 4_05 into one cell and have it update 4_04
automatically so I am not manually changing the formula daily.