<?php
// Create two timezone objects, one for Taipei (Taiwan) and one for
// Tokyo (Japan)
$dateTimeZoneTaipei = new DateTimeZone("Asia/Taipei");
$dateTimeZoneJapan = new DateTimeZone("Asia/Tokyo");
// Create two DateTime objects that will contain the same Unix timestamp, but
// have different timezones attached to them.
$dateTimeTaipei = new DateTime("now", $dateTimeZoneTaipei);
$dateTimeJapan = new DateTime("now", $dateTimeZoneJapan);
// Calculate the GMT offset for the date/time contained in the $dateTimeTaipei
// object, but using the timezone rules as defined for Tokyo
// ($dateTimeZoneJapan).
$timeOffset = $dateTimeZoneJapan->getOffset($dateTimeTaipei);
// Should show int(32400) (for dates after Sat Sep 8 01:00:00 1951 JST).
var_dump($timeOffset);
?>