This http://drupal.org/node/996418 write:
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Post-Install

How can I tell if a page has been cached?
View the page source and scroll to the bottom to find a few stats stored in an "authcacheFooter" JSON object. You may also enable a debugging window for specific users or roles. The admin account (uid #1) is never cached. By default, admin pages and user pages are not cached either.
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1) I activate authcache, authcacheFooter.
2) Activate authcache - Configuration -> Performance -> Authcache
3) Insert code to settings.php:
$conf['cache_inc'] = './sites/all/modules/cacherouter/cacherouter.inc';
$conf['cacherouter'] = array(
'default' => array(
'engine' => 'db', // apc, memcache, db, file, eacc or xcache
'server' => array(), // memcached (host:port, 127.0.0.1:11211)
'shared' => TRUE, // memcached shared single process
'prefix' => '', // cache key prefix (for multiple sites)
'path' => 'sites/default/files/filecache', // file engine cache location
'static' => FALSE, // static array cache (advanced)
'fast_cache' => TRUE,
),
);

In source not found "authcacheFooter" text. Can i check cache work or not?