title: How to detect user's timezone?
body: <p>I need to know what time zone is currently my users are in based on their IP or http header.</p>
  
  <p>I  got many answer regarding this issue, but i could not understood those answer. Some said use <code>-new Date().getTimezoneOffset()/60</code> (<a href="https://stackoverflow.com/questions/13/determining-a-web-users-time-zone/1809974#1809974">from here</a>). But what does it mean? </p>
  
  <p>I have a <code>date_default_timezone_set("Asia/Calcutta");</code> in the root of my (index.php) page. So for this I have to  get the timezone dynamically and set it  in place of <code>Asia/Calcutta</code>.</p>