title: How to record total values with rrdtool
body: <p>I'm pretty sure this question has been asked several times, but either I did not find the correct answer or I didn't understand the solution.
  To my current problem:
  I have a sensor which measures the time a motor is running.
  The sensor is reset after reading.
  I'm not interested in the time the motor was running the last five minutes.
  I'm more interested in how long the motor was running from the very beginning (or from the last reset).
  When storing the values in an rrd, depending on the aggregate function, several values are recorded.
  When working with GAUGE, the value read is 3000 (10th seconds) every five minutes.
  When working with ABSOLUTE, the value is 10 every five minutes.</p>
  <p>But what I would like to get is something like:</p>
  <blockquote>
  <p>3000 after the first 5 minutes</p>
  <p>6000 after the next 5 minutes (last value + 3000)</p>
  <p>9000 after another 5 minutes (last value + 3000)</p>
  </blockquote>
  <p>The accuracy of the older values (and slopes) is not so important, but the last value should reflect the time in seconds since the beginning as accurate as possible.</p>
  <p>Is there a way to accomplish this?</p>