Ciao Artemio,
posto due esempi che consentono solo l'inserimento di numeri nelle Txt1 e txt2:
codice:
Private Sub Txt1_Change()
    
    Dim ix As String
    Dim ixs As String
    Dim ix2 As String
    
    ix = Len(Txt1.Text)
    If ix = 0 Then
        Exit Sub
    End If
    
    ixs = (Txt1.Text)
    If IsNumeric(Txt1.Text) Then
        Txt1.SetFocus
        Else
        MsgBox "Casella di testo Txt1: INSERIRE SOLO VALORI NUMERICI!", vbCritical, "nomedeltuoprogramma"
        ix2 = Mid(ixs, 1, (ix - 1))
        Txt1.Text = ix2
        Exit Sub
    End If
End Sub
'----------------------------------------------------------------------------------
Private Sub text2_change()
    
    Dim txtlen As Double
    
    On Error Resume Next
    
    If Not IsNumeric(Text2.Text) Then
        txtlen = Len(Text2.Text) - 1
        Text2.Text = Mid(Text2.Text, 1, txtlen)
        Text2.SelStart = txtlen + 1
    End If

End Sub