title: Mathematical indicator for the "flattness" of a curve?
body: <p>I am currently working on a computer science project where I have to evaluate charts. The charts are simple lines in an x-y-coordinate-system, given by CSV files. the flatter the curve, the better for me. Now I am looking for an indicator for the "flatness" of these curves.</p>
  
  <p>My first idea was to calculate the first derivative of the function and then calculate the average between two points. If this value is near 0, then the function is pretty flat.</p>
  
  <p>Is that a good idea? Is there any better solution?</p>
  
  <p>Edit:
  <a href="http://tuhrig.de/wp-content/uploads/mathproblem1.jpg" rel="nofollow">Here is a picture</a> as an example. Which curve is flatter between x1 and x2?</p>