Hi,
Have a separate table with one field only that is a long integer and one
record only.
Each time you want to create the PO number, you create the number by using
240-### and concatenating it with the next highest number from that table.
You use a DLookup on that table to get the last used number, then add 1 to
it to get the number you need.
When you have finished and saved that PO number in your form, then you will
update that table and set its one and only record to the number you just
used.
Next time you do the DLookup on that table, you will see that last number
used and can just add 1 to it.

Jeanette Cunningham

If every PO contains the "240-", then I would just drop that from the data,
and display it as part of the label for the PO.  Then, you could just use an
autonumber field for your actual PO number field.

If, however, the prefix of your PO numbers change based on the year or some
other value, then, I would recommend two fields.  One to track the prefix and
another for the suffix.  If you do it this way, then I would make my PO#
field a long integer (rather than an autonumber) and use a technique similar
to that described by Jeanette to get the value of that field each time you
create a new PO.

HTH
Dale

I would avoid autonumber for this, since it will almost invariably create
gaps in the numbering.  One way to simulate an autonumber, but without gaps,
is shown here:
http://www.rogersaccesslibrary.com/download3.asp?SampleName=AutonumberProblem.mdb
There are other options, such as VBA, using the principle outlined in the
example.
If the 240 is constant, I agree with the response that suggested
concatenating the number as needed.  If the 240 is changeable, you will need
to state the rule by which it changes.

The following code will look at the value in your table then add 1 to the
maximum value. The PO Number is a real number but it's formatted the way you
want in the form. In the printed PO, you'll need to either use the value in
the form, or recreate the formatting from the underlying PO number.

Function GetPO() As Long
On Error GoTo Error_Handler

Dim rstID As DAO.Recordset
Dim lngMaxID As Long
Dim db As DAO.Database

Set db = CurrentDb

   Set rstID = db.OpenRecordset("Select Max(PONumber) As MaxID FROM tblPO")
   If IsNull(rstID!MaxID) Then
       'no records yet, start with one
       lngMaxID = 1
   Else
       lngMaxID = rstID!MaxID + 1
   End If

   GetPO = lngMaxID

   Me.txtPONumber = "240-" & Format(lngMaxID, "0000")

Exit_Here:
   rstID.Close
   Set rstID = Nothing
   Set db = Nothing
   Exit Function

Error_Handler:
   MsgBox Err.Number & ": " & Err.Description
   Resume Exit_Here

End Function