title: Adding new datasources to an existing .rrd
body: <p>I have a .rrd db which is collecting data from a temperature gauge. Now I have a second gauge so I'd like to add this new gauge to the existing .rrd database. I tried many times with the "rrdtool tune" command, but after that I run a "rrdtool info" on my database, and I see that there's not the last data source (another gauge) that I tried to insert.</p>
  
  <p>How can I do this?</p>