i don't understand the key slave_running in templates for zabbix

i am using version 1.1.5, and use the template for zabbix.

when i check the graph of MySQL Replication, i fount the key of running-slave allways be 0. so i check ss_get_mysql_stats.php, show like below:

$status[‘slave_lag’] = $row[‘seconds_behind_master’];

Scale slave_running and slave_stopped relative to the slave lag.

$status[‘slave_running’] = ($row[‘slave_sql_running’] == ‘Yes’)
? $status[‘slave_lag’] : 0;
$status[‘slave_stopped’] = ($row[‘slave_sql_running’] == ‘Yes’)
? 0 : $status[‘slave_lag’];

if slave_sql_running allways ‘yes’, slave_running will be slave_lag, and if slave_sql_running == no, then slave_stopped will be empty?

And i find another key running-slave.

So, my question is what’s slave_running and slave_stopped really means?