title: Is "Calculator bug" a code issue?
body: <p>I have seen this bug in many blog posts:
  <a href="http://atifsiddiqui.blogspot.com/2010/11/windows-calculator-bug.html" rel="nofollow">http://atifsiddiqui.blogspot.com/2010/11/windows-calculator-bug.html</a></p>
  
  <p>Is this bug a code bug or a mathematical imprecision ? </p>
  
  <p>I am wondering if its really a bug, How it got undetected for years ?</p>
  
  <p>What should I take care to make sure that it doesn't happen in my custom caculator program.</p>