Sequential numbering in Access

[paddya]

Can anyone here help me with a problem I have in Access.

I'm trying to create a form which would have 3 checkboxes, for Air, Electrical and Mechanical and next to them, an reference number for each.

This reference number needs to be sequential depending on the date

i.e
M01/05/08 would be first mechanical job in may 08
E10/05/08 would be 10th electrical job in may 08

and then the first number would reset to 01 at the beginning of each month. I've been given some code, but I'm a bit of a n00b in access so unsure what to do.

So far, I've created 3 checkboxes with 3 text boxes next to that which references back to the 3 columns in the table, labelled air, electrical and mechanical. I've been told to enter this code

Public Function GenerateProductID(ProdType As String) As String

Dim Prefix As String
Dim StrNextID As String
Dim Rs As DAO.RecordSet

Prefix = Left(ProdType,1) ' (E)lectrical, (M)echanical or (A)ir

'Select all product codes that begin with the prefix and end with the current month and year
Set Rs = CurrentDb.OpenRecordset("Select * From TblProducts Where Left(fldProductCode,1)='" & Prefix & "' And Right(fldProductCode,5) = '" & Format(Date(),"mm/yy") & "';")

'Is there any previous orders for this period?
If Rs.EOF And Rs.BOF Then
   StrNextID = "01"
Else
   StrNextID = Format(Rs.RecordCount +1 ,"00")
   Rs.Close
End If

Set Rs = Nothing

GenerateProductID = StrNextID

Exit Function

but not sure where

and then

Me.ControlName = GenerateProductID(Me.ProductType)

and also

 If Me.CheckBoxA = True Then
  Me.ControlName = GenerateProductID("Air")
  'Add the remaining code here 
End If

If Me.CheckBoxM = True Then
  Me.ControlName = GenerateProductID("Mechanical")
  'Add the remaining code here 
End If

If Me.CheckBoxE = True Then
  Me.ControlName = GenerateProductID("Electrical")
  'Add the remaining code here 
End If

which I'm assuming replaces the previous section.

It was mentioned that I have to create an unbound box for the first function which I've done but not sure where to enter it and guessing that I have to put something on the checkboxes in the 'after update' field.

Can someone help me please.
Thanks