title: SQL Calculate Difference Between Current and Last Value By Timestamp Column
body: <p>I am looking to calculate the difference between the current &amp; last Value organised by the timestamp column?</p>
  
  <p>My table is organised as follows:</p>
  
  <pre><code>MeterID(PK,FK,int.not null), ActualTimeStamp(smalldatetime,not null), Value(float,null)
  
  Meter ID     ActualTimeStamp     Value          
  312514     2013-01-01 08:08:00   72         
  312514     2013-01-01 08:07:00   12 
  </code></pre>
  
  <p>So my answer should be <code>72 - 12 = 60</code></p>
  
  <p>The only solutions I can seem to find are using Row Number which i dont have an option of, if anyone can assist id really apprecieate it as its busting my brain.</p>