Textbox's Value property does not change

Question

I have the following code to run after another control has updated:

[Stock No].Requery

[Debug].Caption = TypeName([Stock No].Value) + " " + Str([Stock No].Value)

If (IsNumeric([Stock No].Value) And [Stock No].Value > 0) Then
    [Stock Status].Caption = "In stock"
Else
    [Stock Status].Caption = "Not in stock"
End If

The value of [Stock No] changes in the form, but [Stock No].Value does not (as seen in the debug label). How can I get the value of [Stock No]?