Public Overrides Function Validate(value As Object, cultureInfo As _
  System.Globalization.CultureInfo) As System.Windows.Controls.ValidationResult
            If value Is Nothing Then
                Return New ValidationResult(False, "Falsche Eingabe")
            End If
 
            Dim i As Single = 0
            If Not Single.TryParse(value.ToString(), NumberStyles.Float, _
              cultureInfo, i) Then
                Return New ValidationResult(False, "Falsche Eingabe")
            End If
 
            If i >= Me.Minimum AndAlso i <= Me.Maximum Then
                Return New ValidationResult(True, Nothing)
            Else
                If i >= Me.Minimum Then
                    Return New ValidationResult(False, "Zu groß!")
                Else
                    Return New ValidationResult(False, "Zu klein!")
                End If
            End If
        End Function

<Binding Path="TEMP_SETPOINT" Mode="TwoWay" _
  UpdateSourceTrigger="PropertyChanged" ConverterCulture="de">