Public Function IsValidCCNum(CCNum As String) As Boolean
Dim i As Integer
Dim total As Integer
Dim TempMultiplier As String

For i = Len(CCNum) To 2 Step -2
total = total + CInt(Mid$(CCNum, i, 1))
TempMultiplier = CStr((Mid$(CCNum, i - 1, 1)) * 2)
total = total + CInt(Left$(TempMultiplier, 1))
If Len(TempMultiplier) > 1 Then total = total + CInt(Right$(TempMultiplier, 1))
Next
If Len(CCNum) Mod 2 = 1 Then total = total + CInt(Left$(CCNum, 1))

If total Mod 10 = 0 Then
IsValidCCNum = True
Else
IsValidCCNum = False
End If
End Function