title: How does an OS X installer package calculate required space?
body: <p>I'm building an OS X Installer package for a product.  When it is run, the 'Select a Destination' pane has an 'Installing this software requires X MB of space' label.  But I can run the same package twice on the same machine, and see the claimed usage vary from, i.e. 85 to 127 MB, neither of which is the actual ~65MB usage of the product.</p>
  
  <p>How does Installer calculate required space?</p>