Public Class SingleDataValidator
        Inherits ValidationRule
 
        Public Sub New()
            Me.Minimum = 0
            Me.Maximum = 1
        End Sub
 
        Public Property Minimum() As Single
            Get
                Return m_Minimum
            End Get
            Set(value As Single)
                m_Minimum = value
            End Set
        End Property
        Private m_Minimum As Single
 
        Public Property Maximum() As Single
            Get
                Return m_Maximum
            End Get
            Set(value As Single)
                m_Maximum = value
            End Set
        End Property
        Private m_Maximum As Single
 
        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
            Try
                i = CSng(value)
            Catch ex As Exception
                Return New ValidationResult(False, "Falsche Eingabe")
            End Try
 
            'If Not Single.TryParse(value, 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
    End Class

<TextBox x:Name="txbTEMP_SETBACK" Grid.Row="3" Grid.Column="1" Width="120" _
  HorizontalAlignment="Left" Margin="10,0,0,0" FontSize="10.667" _
  VerticalAlignment="Center" FontWeight="Normal" >
				 <TextBox.Text>
                    <Binding Path="TEMP_SETBACK" Mode="TwoWay" _
                      UpdateSourceTrigger="PropertyChanged">
                        <Binding.ValidationRules>
                            <validator:SingleDataValidator Minimum="10.0"  _
                              Maximum="30.0"/>
                        </Binding.ValidationRules>
                    </Binding>
                </TextBox.Text>
            </TextBox>