Public Class Form 
[...]
    Private isAction As Boolean = False
 
    Private Sub myProg_Load(sender As Object, e As EventArgs() MyBase.Load
        Me.KeyPreview = True
    End Sub
 
    Private Sub myProg_KeyDown(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.KeyEventArgs) Handles MyBase.KeyDown
        If Me.isAction Then Return
        Me.isAction = Not Me.isAction
        If ((e.Modifiers = Keys.Control) AndAlso (e.KeyCode = Keys.Oemplus _
          OrElse e.KeyCode = Keys.Add)) Then
            zoomIn()
            zeichne_neu()
        ElseIf ((e.Modifiers = Keys.Control) AndAlso (e.KeyCode = Keys.OemMinus _
          OrElse e.KeyCode = Keys.Subtract)) Then
            zoomout()
            zeichne_neu()
        End If
        Application.DoEvents()
        Me.isAction = Not Me.isAction
    End Sub
[...]