Dim factor As Double, i As Integer, sum As Double
 
'Den Faktor umrechnen:
factor = 1
if IsNumeric(TextBox1.text) Then
   factor = Val(TextBox1.Text) / 100
end if
 
'Summe bilden
sum = 0
For i = 2 To 15
    sum = sum + Val(Controls("TextBox" & CStr(i)).Text)
Next i
 
'Multiplikation mit Faktor
textbox16.Text = CStr(sum * factor)