If we wish to get rid of the IF statement, one idea...

Function GenerateCheckDigit(n) As Long
Dim Fg As Boolean 'flag
Dim P As Long
Dim T As Long

'// Odd positions values are doubled
Fg = Len(n) Mod 2 = 1 'Odd?
For P = 1 To Len(n)
T = T + (((1 - Fg) * (Mid(n, P, 1)) - 1) Mod 9) + 1
Fg = Not Fg
Next P
GenerateCheckDigit = (10 - (T Mod 10)) Mod 10
End Function

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Dana DeLouis