Option Explicit

Function sbEAN(s As String, _
  Optional bFullEAN As Boolean = True, _
  Optional bEAN14 As Boolean = False) As Variant
'Calculate or check EAN check digit. Works for EAN-8,
'EAN-13, EAN-14 / GTIN, and for EAN-18 / NVE / SSCC.
'If EAN is given without check digit, it is calculated
'and returned (full EAN if bFullEAn is True or just the
'check digit if False). If full EAN is entered the
'result of the check (True or False) will be returned.
'Source (EN): http://www.sulprobil.com/sbean_en/
'Source (DE): http://www.bplumhoff.de/sbean_de/
'(C) (P) by Bernd Plumhoff 31-Mar-2024 PB V0.3
Dim i As Long, d As Long, m As Long, w As Long
Dim bCheck As Boolean
m = Len(s)
For i = 1 To m
  w = Asc(Mid(s, i, 1))
  If w < 48 Or w > 57 Then
    sbEAN = CVErr(xlErrNum)
    Exit Function
  End If
Next i
If bEAN14 Then
  If m = 13 Then
    bCheck = False
  ElseIf m = 14 Then
    bCheck = True
    m = m - 1 'Calculate checksum without check digit
  Else
    sbEAN = CVErr(xlErrValue)
    Exit Function
  End If
Else
  Select Case m
  Case 7, 12, 17
    bCheck = False
  Case 8, 13, 18
    bCheck = True
    m = m - 1 'Calculate checksum without check digit
  Case Else
    sbEAN = CVErr(xlErrValue)
    Exit Function
  End Select
End If
w = 3
For i = m To 1 Step -1
    d = d + Mid(s, i, 1) * w
    w = 4 - w 'Alternate between 3 and 1
Next i
d = (10 - d Mod 10) Mod 10
If bCheck Then
  sbEAN = Right(s, 1) = d
ElseIf bFullEAN Then
  sbEAN = s & d
Else
  sbEAN = d
End If
End Function