System.InvalidOperationException in Application designer.vb

[Rocky48]

Forget about #19, I must have posted at the same time as #18!

The ValueChanged event handler was created when I double clicked on the control.
So, if I'm correct the form is a Module, therefore any variables I declare in that module will be available to any of the sub-routines.
How does it change if in a ValueChanged event?
Could you give me an example?
Assuming that the way I have written these subs is correct, then:
I have 2 NUD controls and have changed one like so:

 Private Sub nudFSize_ValueChanged(sender As Object, e As EventArgs) Handles nudFSize.ValueChanged
        Dim Fsize As Integer = CInt(nudFSize.Value)
        MessageBox.Show(CStr(FSize))
    End Sub

The other NUD is similar, but says that nudTop has not been declared??

Private Sub nudTop_ValueChanged(sender As Object, e As EventArgs) 
        Dim CTop As Integer = CInt(nudTop.value)
    End Sub

Why does the nudTop have the Handles part?
Why does the FSize one not show the same error?
I did try as InteliSense suggested, but that still said that nudTop had been used before it had been assigned a value?

Dim nudTop As NumericUpDown = nudTop