Invalid References

In config.inc.php the are some references that i can´t see any valid reference to them in the crm

$includeDirectory = $root_directory.'include/';

$limitpage_navigation = '5';

$calculate_response_time = true;

$default_user_is_admin = false;

$disable_persistent_connections = false;

$translation_string_prefix = false;

$cache_tab_perms = true;

$disable_stats_tracking = false;

$CHAT_DISPLAY = 'true';

$CALCULATOR_DISPLAY = 'true';

$WORLD_CLOCK_DISPLAY = 'true';