Function TwosComplement(ByVal rngNum As Range) As String
'written by David Coutts
'26/11/2004
    
    Dim outVal As String
    Dim i As Integer, lenOrig As Integer
    Dim myNum As Long
    
    
    'Invert the Binary
    For i = 1 To Len(rngNum.Value)
        outVal = outVal & Abs((CInt(Mid(rngNum.Value, i, 1)) - 1) Mod 2)
    Next i
    
    Dim bolDone As Boolean
    'convert from binary to integer
    For i = Len(outVal) To 1 Step -1
        myNum = myNum + CInt(Mid(outVal, i, 1)) * 2 ^ (Len(outVal) - i)
    Next i
    myNum = myNum + 1
        
    'convert back to binary
    For i = Len(outVal) - 1 To 0 Step -1
        If myNum - (2 ^ i) >= 0 Then
            myNum = myNum - (2 ^ i)
            TwosComplement = TwosComplement & "1"
        Else
            TwosComplement = TwosComplement & "0"
        End If
    Next i

End Function