title: RRDTool data source type selection
body: <p>I have a question related to RRDTool DST. I need to create a database in such a way that even the data is the same (for example, I have six entries per hour with the same value). RRDTool must calculate the AVERAGE of this data.</p>
  
  <p>I'm creating database with following command:</p>
  
  <pre><code>rrdtool create test.rrd --step 15 DS:na:GAUGE:15:0:U RRA:AVERAGE:0.99:1:244 RRA:AVERAGE:0.99:24:244 RRA:AVERAGE:0.99:168:244 RRA:AVERAGE:0.99:672:244 RRA:AVERAGE:0.99:5760:374
  </code></pre>
  
  <p>And I'm updating database with following command:</p>
  
  <pre><code>rrdtool update test.rrd 1296231519:0.6039 
  </code></pre>
  
  <p>After making 10 entries with the same value (changing timestamp but the same value), I do <code>rrdtool dump test.rrd test.xml</code>, but I don't see any data... It does not contain the 10 entries.</p>
  
  <p>After making 10 entries with a different value (changing timestamp and changing value), I do the dump of database and there are the 10 entries I have done.</p>
  
  <p>What I'm doing wrong? Maybe DST 'GAUGE' is wrong on creation of rrd?</p>