title: Paper_Trail: Show Diff Between Versions
body: <p>I'm new to Rails...using RubyMine as an IDE. </p>
  
  <p>I have Paper_Trail saving previous versions of the data "xoi_qb". My view is currently showing the current and previous data as I'd like, but I would like to show the diff between the current version "xoi_qb" and the previous version "xoi_qb". For instance, the current version may be "97" and the previous version may be "94", and I would like to display "XOI +/-: +3". I would like to display this difference and add the "+" or "-" based on the positive or negative change. </p>
  
  <p>In my model, Paper Trail is set to create versions like this:</p>
  
  <pre><code>  def get_xoi_qb
      xoi_qb = []
      self.versions.each do |version|
        unless version.reify.nil?
          xoi_qb &lt;&lt; version.reify.xoi_qb
        end
      end
      return xoi_qb
    end
  </code></pre>
  
  <p>And in my HTML set to display the versions like this:</p>
  
  <pre><code>  &lt;th&gt;Previous XOI&lt;/th&gt;
    &lt;table&gt;
      &lt;% @quarterback.versions.each do |version| %&gt;
          &lt;tr&gt;
            &lt;td&gt;&lt;%= version.reify.xoi_qb %&gt; dated &lt;%= version.created_at %&gt;&lt;/td&gt;
          &lt;/tr&gt;
      &lt;% end %&gt;
  </code></pre>
  
  <p>Not sure how to show the difference between the two.</p>
  
  <p>Really appreciate the help.</p>