title: Input of a double precision number
body: <p>I writing some astronomical programs, and I have available the source code for Jeffrey Sax's implementation of the algorithms in Meeus' book Astronomical Algorithms.</p>
  
  <p>One of the functions he has written is ReadReal(), which obtains a real number from the user (via the keyboard or terminal). An extract from this function looks like this:</p>
  
  <pre><code>scanf("%lf", &amp;r);
  return r * 1.000000000000001;
  </code></pre>
  
  <p>The multiplication by the constant on the second line evidently has something to do with rounding but I cannot see exactly what. I have searched for answers, and the constant appears in many places on various sites but not in this context.  Does anyone have experience of this or know what is going on here? Is it important?</p>
  
  <p>Thanks for any help.</p>