A Beginners Naivety - Varaibles

[librarat]

I'm just learning WPF apps and have been looking for a good tutorial on how variables work within the WPF model, but really haven't been able to find something. Subsequently, I'm a bit stuck :S

I feel like I'm trying to do something basic here, but maybe I'm just off my rocker. All I'm trying to do is onSelectionChanged of a dropdown, run function XXX. Function XXX, at run, populates a variables then writes the variable to a label. I'll post code snippets. But what am I missing?

DropDown Code

<ComboBox Canvas.Left="223" Canvas.Top="261" Height="23" Name="userTempScale" Width="54" Background="{x:Null}" BorderBrush="#FF992907" BorderThickness="0" Foreground="#FF992907" HorizontalContentAlignment="Center">
            <ComboBoxItem Content="F" IsSelected="True" />
            <ComboBoxItem Content="C" />
            <ComboBoxItem Content="K" />
            <ComboBoxItem Content="Re" />
            <ComboBoxItem Content="Ra" />
        </ComboBox>

Dropdown Handler Code

    Private Sub userTempScale_SelectionChanged(ByVal sender As Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs) Handles userTempScale.SelectionChanged
        calculateTemps() ' Update our Temps 
    End Sub

Function XXX code

Public Function calculateTemps() As Action
Dim tempscale As String = userTempScale.SelectedItem.ToString
If tempscale = "F" Then
fah_label.Content = tempscale
endif

Like I said, pretty basic but I seem to be missing a connection between WPF and WinForms. Anyone got a wrench to smack me over the head with?