title: WPF bind numeric values in TextBoxes to change relative to each other
body: <p>How to bind multiple WPF TextBoxes holding numerical values to change the same absolute amount if one of the TextBox value is changed?</p>
  
  <p><img src="https://i.stack.imgur.com/0ouiv.png" alt="Multiple TextBoxes"></p>
  
  <p>Lets say I have the above UI. If the CheckBox is not checked, I need the regular binding to ViewModel property (this is what I have now):</p>
  
  <pre><code>&lt;TextBox Text="{Binding Value1}" /&gt;
  &lt;TextBox Text="{Binding Value2}" /&gt;
  &lt;TextBox Text="{Binding Value3}" /&gt;
  &lt;TextBox Text="{Binding Value4}" /&gt;
  &lt;TextBox Text="{Binding Value5}" /&gt;
  &lt;CheckBox Content="Relative Changes Constant" IsChecked="{Binding UseRelative}" /&gt;
  </code></pre>
  
  <p>If the CheckBox is checked however and the value in any TextBox is changed, I need to have all other TextBox values updated the same relative amount up or down.
  For example, if the 2nd TextBox value is updated from 25 -> 30. The other 4 TextBox values should then become 39, 26, 30 and 32 (increase by 5).</p>