Function Azalea_Code_39_checkdigit(ByVal Code39 As String) As String
' C39Tools 16may12 jwhiting
' Copyright 2012 Azalea Software, Inc. All rights reserved. www.azaleabarcodes.com

' Creating a Code 39 barcode with the optional mod 43 check digit in Excel
' Your input, Code39, is a string to be encoded as a Code 39 symbol that includes the mod 43 check digit.
' yourData must be the Code 39 character set. Input error checking is your responsibility.
' The standard Code 39 character set is: A-Z (upppercase), 0-9, $ % + - . / and the space character.

  Dim i As Integer                   ' our loop counter
  Dim subtotal As Integer            ' the check digit subtotal
  Dim temp As String                 ' a temporary placeholder
  
  temp = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. $/+%"

  ' calculate the mod 43 check digit
  For i = 1 To Len(Code39)
    subtotal = InStr(temp, Mid(Code39, i, 1)) - 1 + subtotal
  Next i

  Azalea_Code_39_checkdigit = Mid(temp, (subtotal Mod 43 + 1), 1)

  ' Excel: B1=Azalea_Code_39_checkdigit(A1)
  ' Or put another way, yourContainer.text=Azalea_Code_39_checkdigit(yourInputString)
  
End Function