title: show a exactly Height of text in a TextField
body: <p>I have to program a see test for an optician. So they need that the Numbers are exactly have a specific height.
  He has a IPad ans streams it to a TV. I know i must consider the PPI of the TV. Here is my Code :</p>
  
  <pre><code>func calcPoints() -&gt; Float {
      // he gives the Visus with a TextField
      let visus = Float(textFieldVisus.text!)
      // Here you put in the PPI of the device
      let ppi = Float(textFieldDPI.text!)
      // Calculate the lenght of the Number
      let lenght = ((0.29 * 5) / visus!) * 5
      // Calculate the Points (because TextFiels work with Points)
      let points = ((ppi! / 25.4) * lenght) * 0.75
      // here you divide with 2 because you have a retina Display on the IPad
      return (points / 2)
  }
  
  func passeUIan() {
      // Now i can give the Points to the TextField
      textField1.bounds.size.width = CGFloat(calcPoints())
      textField1.bounds.size.height = CGFloat(calcPoints())
      textField1.font = UIFont(name: (textField1.font?.fontName)!, size: CGFloat(calcPoints()))
  }
  </code></pre>
  
  <p>but when i measure off the lenght on the TV it is wrong.
  Normaly it must be 7.25mm but it is approximately 9mm.
  i dont know what is wrong. I search for this problem since 2 weeks...</p>