Не распознает дробные числа

Private Function result(a As Double, s As Double, z As String) As Double
 
        Select Case z
            Case "+"
                s = s + a
            Case "-"
                s = s - a
            Case "/"
                s = s / a
            Case "*"
                s = s * a
            Case "mod"
                s = s Mod a
 
        End Select
        result = s
    End Function

Private Sub btnPlus_Click(sender As Object, e As EventArgs) Handles btnPlus.Click
        Dim a As Double, s As Double 
        Dim z As String
        
        a = Val(txtNumber1.Text)
        s = Val(txtResult.Text)
        z = lblZnak.Text
        txtResult.Text = result(a, s, z)
        lblOperator.Text = lblOperator.Text & txtNumber1.Text & btnPlus.Text
        lblZnak.Text = btnPlus.Text
 
        txtNumber1.Clear()
       
    End Sub

TextBox1.Text

a = Val(txtNumber1.Text.Replace(",", "."))
        s = Val(txtResult.Text.Replace(",", "."))

        Dim Val1, Val2, Res As Double
        Val1 = TextBox1.Text
        Val2 = TextBox2.Text
        Res = Val1 + Val2
        MsgBox(Res / 2 & " - среднее арифметическое?")

Globalization.CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator