title: Cannot figure out how to evaluate series subscript
body: <p>Can someone please help me to understand the following piece of code?
  Ok, so I'm checking hlc3 on a Swedish stock and plotting the result from an XSA function found in one strat on tradeview. I understand series and how that easily can be confused by arrays.
  Now to the point, my input src (hlc3)</p>
  <pre><code>src = 720.7
  variable ma, still = 720.7 
  but variable b[1] changed it to 59... 
  </code></pre>
  <p>where does 59 come from?</p>
  <pre><code>xsa(src,len,wei) =&gt;
  
      sumf = 0.0
      ma = 0.0
      out = 0.0
      b = 0.0
      sumf  :=  nz(sumf[1]) - nz(src[len]) + src
  
      ma  :=  na(src[len]) ? na : sumf/len
  
      b := na(b[1]) ? ma : b[1]
      b[1]
  
  al = hlc3
  
  plotchar(xsa(al,1,1), &quot;Bar Index&quot;, &quot;&quot;, location = location.top)
  </code></pre>
  <p><a href="https://i.stack.imgur.com/CDZXg.png" rel="nofollow noreferrer">Image from tradeview with value</a></p>