Не работает форма для уравнения N=Log(1-Pg)/Log(1-Pi)

Private Sub ComboBox1_Change()
Debug.Print Pi
Debug.Print Ni
End Sub
 
Private Sub CommandButton1_Click()
Dim delP As Double
Dim Pi As Double
Dim Pk As Double
Dim Pg As Double
Dim Pn As Double
Dim a As Variant
Dim b As Variant
Dim Ni As Variant
Dim P As Double
Pi = TextBoxPi.Value
Pk = TextBoxPk.Value
Pg = TextBoxPg.Value
delP = TextBoxdelP.Value
Pi=Pn
a = WorksheetFunction.Log10(1 - Pg)
Do Until Pi > Pk
b = WorksheetFunction.Log10(1 - Pi)
Ni = a / b
Pi = P + delP
Loop
End Sub
 
Private Sub CommandButton2_Click()
End
End Sub
 
Private Sub ListBox1_Click()
Debug.Print Pi
Debug.Print Ni
End Sub
 
Private Sub OptionButton1_Click()
ListBox1.Visible = True
ComboBox1.Visible = False
End Sub
 
Private Sub OptionButton2_Click()
ComboBox1.Visible = True
ListBox1.Visible = False
End Sub