title: How to get the value of a specific column in a specific line in any time of processing in gnuplot?
body: <p>I got a data file in the format like this:</p>
  
  <pre><code># begin
  16 1
  15 2
  14 3
  13 4
  12 5
  11 6
  </code></pre>
  
  <p>Now I want to use gnuplot to draw a line through the points: </p>
  
  <pre><code>(1, (16/16))  (2, (16/15))  (3, (16/14)) ...  (6, (16/11)) 
  </code></pre>
  
  <p>As you see, the x axis is the range [1:6] and the Y axis corresponds the values obtained from the number in the first line at the first column(ie. 16 in this example) divided by the number in each line at the first column. </p>
  
  <p>The problem is that I don't know how to get the value of the number at the first column in the first line (16), so that I could do something like </p>
  
  <pre><code>plot "datafile" using 2:(16/$1) with linespoints
  </code></pre>
  
  <p>I have done a lot of search about how to achieve that but with no luck. It seems that gnuplot doesn't provide some flexible ways to allow arbitrary data selection. Any ideas how to do that? Or maybe I just got stuck into a not so common problem?</p>
  
  <p>Thanks for your help in advance.</p>