title: How to set second yAxis scale according to data from first yAxis
body: <p>I have an odd request. My boss wants me to improve an existing chart with a second axis.
  <img src="https://i.stack.imgur.com/rD2Q4.png" alt="Here is my existing chart"></p>
  
  <p>The blue area must define the scale of the second axis, like a percentage of completion for the reading of the green area. <strong>The 100% value must be at the maximum of the blue area</strong>. I can collect the highest value of the blue area without any trouble, but I don't know how to set the properties of the second axis according to this value. The thing is that the second axis does not have any data associated, therefore, he isn't shown...</p>
  
  <p>Any idea ?</p>
  
  <p>PS : I tried to be as clear as possible, but maybe that was not the case. Don't hesitate to tell me if you need more explanations.</p>