One way to consider

Earmark a cell say, A1
to contain the numbers: 121, 128, etc

Then we could put
in say, A2: =INDIRECT("[SDS.xls]we"&A1&"!$L$3")

If A1 contains: 121
A2 will return the same as: =[SDS.xls]we121!$L$3

If A1 contains: 128
A2 will return the same as: =[SDS.xls]we128!$L$3

So you can control what's returned in A2
via easily changing the input in A1

And you could also easily create a Data Validation (DV)
to select the week#s in A1 (instead of inputting)

Just select A1
Click Data Validation
Settings:
Select under "Allow:" : List
Put in "Source:" : 121,128,135,142,149,156, etc
Click OK

Or, use a named range as the DV source

In another sheet, say Sheet2
------------------
Put in A1: 121
Put in A2: 128
Select A1:A2, fill down to say, A20
Name the range A1:A20 as : MyList

Then do the same DV steps for A1 above,
with the exception for step "Put in "Source:"

Replace with:
Put in "Source:" : =MyList
--
Rgds
Max
xl 97
---
GMT+8, 1° 22' N 103° 45' E
xdemechanik <atyahoo<dotcom
----
"outlook help" wrote in message
...
is there a way to create a formula that changes the name of a sheet within
another formula. In other words, the following is a reference to an
external
workbook within an IF Function -- '[SDS.xls]we121'!$L$3. The sheet name
we121
will change on a wkly basis by 7 days. I would like to have the formula
automatically look at the worksheet that is we121+7 OR we128. Is it
possible?

Thank you.