<UserControl x:Class="SingleValueCtrl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/" & _
               "006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:WpfApplication1"
             mc:Ignorable="d" 
             Height="Auto" Width="Auto">
    <UserControl.Resources>
        <local:NullableDecimalConverter x:Key="nullDecConv"
DecimalPlace="{Binding DecimalPlaceOfControl,RelativeSource={RelativeSource" & _
  "Mode=FindAncestor,AncestorType={x:Type local:SingleValueCtrl}}}" >
        </local:NullableDecimalConverter>
    </UserControl.Resources>

    Protected Overrides Sub OnPropertyChanged(e As _
      System.Windows.DependencyPropertyChangedEventArgs)
        If e.Property.Name = "DecimalPlaceOfControl" Then
            Dim conv = CType(Me.Resources("nullDecConv"), _
              NullableDecimalConverter)
            conv.DecimalPlace = CType(e.NewValue, Nullable(Of Integer))
        End If
        MyBase.OnPropertyChanged(e)
    End Sub