title: Prometheus: How does the rate function calculate per second rate when scrape interval is longer?
body: <p>From Prometheus documentation rate function does the following:</p>
  
  <blockquote>
    <p>rate(v range-vector) calculates the per-second average rate of
    increase of the time series in the range vector.</p>
  </blockquote>
  
  <p>How is that possible when scrape interval is longer like <code>15 seconds</code>? I mean how does Prometheus estimate "per-second" value when the data points are at least 15 seconds far away?
  I assume that the change is estimated to be uniform in the scrape interval but want to be sure.</p>