title: Google Checkout Accessing Merchant Calculations Callback
body: <p>I'm implementing the Google Checkout service into my web service using the XML api. I have the cart request and all of that setup, and am using the Merchant Calculations api for shipping (My service does shipping calculations)</p>
  
  <p>I'm having difficulties figuring out how to access the  response that is sent to my server with the buyer's address / other personal data for the order and determining their shipping request.</p>
  
  <p>Is  being sent in the header? as a POSTS value? GET? How do I access it.</p>
  
  <p>I'm developing using PHP</p>