title: Why does Grafana return different values for a counter metric on different ranges
body: <p>My Grafana dashboard returns different values for a counter metric with different ranges. I think it's not supposed to.</p>
  
  <p>The metric is <code>sum(notification_publisher_mail_total) - sum(notification_publisher_mail_errors)</code>. It should be a constant in different ranges since it is the sum of two counters.</p>
  
  <p>Here are my examples:</p>
  
  <p><a href="https://i.stack.imgur.com/nDJ7Z.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nDJ7Z.png" alt="With today range"></a></p>
  
  <p><a href="https://i.stack.imgur.com/N3dOr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/N3dOr.png" alt="With this week range"></a></p>