title: Advanceable historical stream and live stream in Rx
body: <p>I have a hot observable that I normally implement using a normal <code>Subject</code> underneath, so that those interested could subscribe to a live a stream of notifications. </p>
  
  <p><em>Now I would like to keep that live stream, but also expose a historical stream of all the events that have been AND have absolute times attached to those notifications to know when exactly they happened AS WELL AS allow the subscribers to advance the historical stream to any point in time before replaying the chronology.</em> </p>
  
  <ul>
  <li>I believe most of this could be achieved with a <a href="http://msdn.microsoft.com/en-us/library/system.reactive.concurrency.historicalscheduler%28v=vs.103%29.aspx" rel="noreferrer">HistoricalScheduler</a> and its AdvanceTo method, but I'm not sure exactly how?</li>
  <li>And is use of <a href="http://msdn.microsoft.com/en-us/library/hh228977%28v=vs.103%29.aspx" rel="noreferrer">Timestamped</a> to save the times of the events needed?</li>
  <li>And is a <a href="http://msdn.microsoft.com/en-us/library/hh211810%28v=vs.103%29.aspx" rel="noreferrer">ReplaySubject</a> needed to cache the live stream into historical records which could then be played back using the HistoricalScheduler?</li>
  </ul>
  
  <p>How exactly can those two streams be implemented for the same source, or in other words, how can the below be appropriated to the current requirements?</p>
  
  <p><img src="https://i.stack.imgur.com/lupBx.png" alt="how to save time in .net"></p>
  
  <p>[ see <a href="http://blogs.msdn.com/b/rxteam/archive/2012/06/14/testing-rx-queries-using-virtual-time-scheduling.aspx" rel="noreferrer">"Replaying the past"</a> heading ]</p>