title: How to set custom y axis Chartkick
body: <p>So, I tried using <a href="https://github.com/ankane/chartkick" rel="nofollow">Chartkick</a> on my project, and it all work fine, but there is one thing I can't make it done, which is set custom y axis. What the tutorial said was about using <code>count</code>. While I need some kind of this code:</p>
  
  <pre><code>@foo = Bar.select("SUM(payment_amount)").group(:payment_date)
  </code></pre>
  
  <p>So I need that the y axis consist of cumulative amount of those data, how should I do this with <strong>Chartkick</strong>?</p>